You probably are cutting it a bit fine, but I wouldn't worry too much about it. An extention for the Fiance Visa isn't terribly difficult to get if you need it. And I think the rules state that you have to be married within six months from the issue of the visa, but unless I'm mistaken, you don't have to get the FLR within that amount of time. (EnglandsYank, you're thinking of the conversion from FLR to ILR...that bit of the process does require you to apply four weeks before the FLR expires.)
My Finacee Visa was issued the very day they got my application, even though it wasnt offically approved and sent back to me for two weeks after that. So you may want to hold out if you can and delay your application slightly.
Also, you mentioned your wedding date being 24 Feb, and wanting to send your application off on the 25th. Unfortunately this won't be possible because you'll need your original marriage certificate and here in the UK, these usually take 7-10 days to get to you. So keep that in mind too!