most likely of explicit time lapse or maybe implicit time skip where a comic or animation would show, or at least heavily imply that the sex / intercourse been happening for a few hours;
some comics uses those a few panel separators that fade from daytime-blue to afternoon-orange and sometimes night-time-navy, if you seen a comic with this tyme lapse, you'll understand what I'm saying
and some animations would either fade-to-black for a few seconds or use a short montage with a variety of poses and the like
of course for this tag to be valid, the action must still be happening when the jump-cut ends, sleeping before the fade and waking up after the fade wouldn't count
here's a few example of what this tag should include
post #637474
post #2961655
post #3188485
post #1305078 and post #1305565 and post #1305565
post #1163964
post #1471689
here's a few example where the tag might fit
post #2071390 and post #2071393
post #2239684
post #3003073
post #1147118 and post #1763459
post #2676475
here are a few examples of post to not include such tag
post #2169171 and post #2709924
post #2312228 and post #2329548
(WARNING! some post include contingency tags and might be in some people's blacklist!!)
I hope can get my idea across, I'm not very good with words, but basically what I said above, a tag for sex / intercourse that takes a few hours in-universe
that's my 2-cents, just an idea, maybe a suggestion? if anyone want to create a tag or I get some moderator's vlessing to do it myself