JetGumRadio: You can mess around all you want. if you miss a time limit you just wait until the next day at the same time without any consequence. You can do that as many times as you want. There are certain points where you can't mess around in the town and have to get somewhere quick but you will know when that is. If you need to skip to the next day you just find a bed to go to sleep or smoke cigarettes.
You should look into getting the radio near the start of the game that enables fast travel to any location you have visited at least once, that helps a lot. If you miss a side quest you can replay any chapter at any time. Only thing is you can't save and have to complete it and everything will be brought over to your current game.
Darklord666: Theoretically yes, but don't forget this game breaking
bug:
" Disappearing Keys
This is a serious glitch that forces players to restart the entire game. This glitch involves replaying chapters while you have a key you need to use in your current saved game in your inventory. If you are in Chapters: 5, 9 or 23 and have been given or found a key item that needs to be used later to unlock something in the chapter DO NOT, and I repeat DO NOT try and replay any earlier chapter from the main menu before using said key. If you do the key will disappear from your inventory with no way of ever obtaining it again leaving the only solution to re-start the entire game over and lose all your progress and items. "
There's a guy on the Steam forums who's trying a hex editor on the savegame and he found some interesting stuff. (Like forcing the game to replace York with another character and such). I think it MIGHT be posible to add the missing key back again by editing the savegame this way. Maybe even come up with a small batch file or fix that would do it for you.
