This is so wildly dependent on circumstance, that I can't say what's ideal in any one. A fifteen minute quickie can be a good way to relieve your tension before bed, or even a five minute quickie in the car before a concert can be amazing because it is so intense. On the other hand, I have had sex for between four and five hours at a stretch and had it also be amazing. Longer than that if you don't count rest or food breaks as starting a new session.
Coffee...
I should probably stop doing that if I don't want to wither into dehydrated husk of a human, but... some days my position on that matter is still "Eh. Whatever".
About fifteen minutes ago.
Ethical non-monogamy is complicated as fuck, but ultimately worthwhile.
Cold water. I am dehydrated from... vigorous physical activity.
This is completely situational, to me. Factors in that decision include (but are not limited to) who I'm fucking, if we are fluid bonded or barrier protection is necessary with intercourse, where I'm fucking them, how much energy I have, and just generally my mood that day.
Maybe some toast or something. Been snacking all day.
Orgasm(s) or sleep, depending on what kind of headache.
Cider and a shot of whiskey.
(Defense against) the Dark Arts
A symphony of coughing. Everyone who lives in my house is sick.
I've never been sure if it is the accent or the person's specific voice that gets me.
Two, three hours. Not exactly sure. Anymore I make it a general policy not to fuck someone on a first date. At an event like a big festival I'll fuck someone pretty much right away, as long as I'm attracted to them, they are attracted to me, and there's adequate protection to be had.