Once you're in the predebate menu, your arguments are "locked-in". You gotta change 'em prior to invocation.
The days remaining are partially replenished at the beginning of each part, although not necessarily by a fixed amount. You have my guarantee that you'll be given enough time to complete said part, even if you run the clock down to almost zero in the prior one.
There are ways to get more money. One, you'll encounter without doing anything particularly fancy, so just keep playing and you'll find out.