I'm going to give away the whole plot here; as I say, that shouldn't be a problem (since it will never be performed again), but SPOILERS HO!
The basic premise is that it's a musical about a musical: a theatre group are preparing for a West End show, set during WW2. However, this didn't lead to any kind of meta-fiction, and we didn't see much of the "inner" play, it was just a way of including songs from different decades. Similarly, the title comes from one of the songs in Rent (which I haven't seen), aka "525,600 minutes".
This did actually fit into the main plot quite well, because one of the characters was narrating a year in flashback, so he could provide brief summaries whenever they skipped forward a few months (a bit like Ferris Bueller). However, this got a bit clunky when they wound up with a nested flashback: there was one scene set at a party, and the next scene was set the morning after, but then they reversed direction to go back to something that happened at the end of the party. In retrospect, I think this was mainly done so that they could close the curtains and let the stage crew change the scenery (switching from an indoor room to a garden), but I'm sure there was a better way of handling that.
While the characters are rehearsing for their performance, there's also a romantic sub-plot going on. Basically, Max (the producer) had moved to America 20 years previously, and said that he'd get in touch with his girlfriend once he was settled, then she could join him. However, that was the last she heard from him until he returned to London to put on this new play. Over the course of the year, they gradually rebuild their relationship, and get engaged. Max started to get cold feet, and asked his fiancee a few times whether she was sure about this, so I assumed that this was leading somewhere: either he'd overcome his fears and marry her, or he'd run off to America again. However, the play ended without any kind of resolution there, which was a bit odd.
Anyway, this subplot meant that they used one of my favourite songs: What If?, as performed by Kate Winslet for A Christmas Carol.
This was something of a mixed blessing. The actress had a good voice, and I think the song is actually a lot more poignant when it comes from someone in her 40s; when she wonders how different her life could have been if she'd followed Max rather than letting him go, it really makes sense that this would have had deep consequences. By contrast, Kate Winslet was 26 when she performed the song, so although it's linked to older characters in the Dickens story (i.e. Scrooge and his ex), she still appears prominently in the video. Having said that, I still prefer Winslet's version, which may simply be because of the higher production values. The main point here is that if you do a cover version then you invite comparisons to the original version, and I think it's more obvious with a solo singer than it is for a group.
As I said, they had some songs from different decades, particularly in the "inner play". We didn't see a great deal of that, but there was one particular scene which was split between countries: the women were in London, while the men were in the trenches, and they all listen to Vera Lynn songs. This seemed a bit odd to me, since I'd normally associate trench warfare with WW1 (particularly for the British army); that's also the correct period for songs like "Pack up your troubles in your old kit bag". However, there were quite a few elderly people in the audience who seemed to particularly enjoy that part of the performance, and they're better qualified than I am to comment on any historical inaccuracy.
More generally, I've seen quite a few musicals, and it's fairly common for the spoken sections to just move things along ready for the next song. However, those songs normally have a unifying theme, particularly if they were written specifically for this musical, and they can advance the plot on their own. In this case, picking songs from all over the place did feel a bit haphazard (e.g. Christmas carols in June), and it led to the cliche of "We know a song about that!" I suppose that the same thing could be said for musicals that are based on songs from a particular pop group (e.g. Abba, Queen, Take That), but I haven't seen any of them, and at least the songs will all have something in common.
In a way, this play reminded me of High School Musical: as well as preparation for a performance (that we never actually see), the characters have a tendency to spontaneously break into song. That's fine by me; I'm happy to suspend my disbelief there, as a genre convention. The problem came when they felt the need to justify this. For instance, there's a Christmas party at one point, so various people perform songs for each other. My friends have done similar things in the past, by preparing "party pieces" for New Year, so that's plausible. The problem is that the characters performing each song were facing the theatre audience, so they had their backs to the other characters; in the context of the party, that seems rather odd. Similarly, there was another scene where a group of people plan a surprise birthday party for Max's girlfriend; in honour of the occasion, a few of the women then perform a song and dance routine that they've prepared. This would be fine, except that Max's girlfriend is one of the people performing it; how did she do that, if she didn't know that the party was happening? I think that when the writer tried to be clever and explain things, he just made it worse, by drawing attention to these flaws. Unless you have a really good idea (like in Enchanted), it's better just to tell people to accept it, and not think about it too much.
Due to the limited number of people in the cast, there was a bit of doubling up on roles. That's fair enough, and I've seen the same thing in various other plays; in fact, I've done a couple of dual roles myself. However, you do need some way to identify which character is which, even if it's as simple as different hats. One of the actors had at least three different parts, but I had to pay close attention to keep track of which was which. There were two girls who auditioned for the inner play but were turned down; later on, they were present in the cast, so were they now playing different parts, or did they get back in? Since it was a relatively important plot point (or at least an excuse for a song) when they were upset about being rejected, it was a bit jarring to think "Hang on, what are they doing there?" Similarly, it seems as if the same group of people were taking part in the play and spending all their free time together (e.g. at Christmas parties); that may be accurate, given what I've heard about the incestuous nature of some theatre groups, or it may mean that there was more doubling up, but it was hard to tell.
During the Christmas party, they brought in a conjuror to do a few tricks, and he was very good. This was where they blurred the fourth wall a bit, since he involved the theatre audience in his "pick a card" routine: he'd get two different people to choose cards and show them to the rest of the audience (without showing him), then put them back in the deck. Back on stage, he then threw the entire deck of cards in the air, and impaled two cards in mid-air with a knife. This led to an unintentionally funny scene:
Conjuror: "Madam, what was your card?"
Lady in audience: "Er, the 5 of Spades. I think."
Conjuror: "Ok, did anyone else notice what card it was?"
[General mumbling from audience.]
Conjuror: "Was it, perhaps, the 5 of Clubs?"
Lady in audience: "Yes, I think so."
He did get the right card, and I felt a bit sorry for him; it's a bit less impressive to ask "Is this your card?" if the other person says "Dunno, I can't remember". Ah well, that's the joy of live performances, and the second audience member had a better memory.
The other general issue was that they had a few technical problems. There were a few microphones on the stage, but at times it sounded like someone changing gear when they're first learning to drive (*crunch* *screech*). However, I think that they should have been able to perform without the mikes. Since this was an amateur performance, it's unfair to compare it to a West End show, but I'm comparing it to the school plays we did at CH: the theatre there could hold about 800 people (spread across three levels), and we all learned to project our voices without shouting. In this case, there were only about 40 people in the audience for the matinee performance, so volume shouldn't have been an issue.
Anyway, all in all it was a pleasant way to spend my time, but I think there are lessons to be learned.