A few questions about boil times and recipes

Hey folks, I'm sure this is either already covered (although I couldn't find it after lurking for a few days) or doesn't matter (seems like a lot of stuff can just be winged!).

I'm pretty new to homebrewing (only 2 batches) and I've been looking around for my next batch and recipe and noticed that a lot of recipes say to add hops at specific times. For example:

XXXXX at 15 min
YYYYY at 60 min

My questions is, how much longer after the 60 minute do you boil if it doesn't say? I understand that you are trying to use the second hop addition to flavor so you don't want to boil too long else they will change the flavor profile (or at least that's my current understanding). Is there a thumb-rule for this?

Thanks folks! Will continue to read, and you'll have a lot more questions coming from me soon!

The convention is to go backwards. The addition times reflect rime left before flame out. Additional boil time will be in the instructions. For example

Boil time 75 min
0.5 oz Cascade (8.8 acid) @ 60 min
1 oz Cascade (8.8 acid) @ 15 min
1 oz Simicoe (6.5 acid) @ 5 min

The Simicoe hops are aroma hops added just before you shut off the heat. If there are no other boil instructions you can assume that the first hop addition is just after boiling starts. However, no one is to say the recipe is complete or well written. There may be cues that a longer boil is needed. But I'd say that is pretty unusual.

The 60 minute addition is the bittering addition and should be in the longest. Add shortly after the break (froth and potential of boiling over) has past. These hops should be in the boil for at least 60 minutes. Boiling shorter will lessen the bittering of the beer and upset the balance. Leaving them in for longer is OK as most of the bittering compounds are extracted by 60 minutes.

15 minute hops should be added with 15 minutes to go. 5 minute addition should be added with 5 minutes to go. You should not boil the wort after these times are up; these are flavor and aroma additions, and the delicate oils will evaporate if boiled for longer.

When you reach the 0 minute time, the heat should be shut-off, the pot removed from the heat source, and the lid placed on. Once boiling stops, you will not lose any of the delicate hop oils, so it is not critical (from a hop extraction point of view) to cool immediatly. Some people like to steep the wort after the boil (between 15 and 30 minutes), before cooling as they believe it extracts more aroma from the hops.