At Peak Speed I can get in and out in an hour: 15 min to groom/tack up, 15 min to untack/pick feet/put away, 30 min to ride. I compromise on how clean the pony is before riding, how clean its tack/my boots are after, and how nicely my stuff is arranged (figure-eighted, etc.) when put away; I don’t compromise on picking feet well both before and after, hosing in summer or currying out sweat marks in winter, and cleaning up after myself in common spaces (though I do groom in the stall specifically to avoid this as much as possible.)
If I have two and I’m doing a fitness day, I’ll pony one, which saves needing to groom and tack the 2nd one at all beyond picking feet and attaching an appropriate headstall. An hour is still never enough time to deal with two at all, but if I’m dealing with two anything under an hour per horse is gravy.
I’ve been observed getting on a horse in some creative attire; I always wear boots with a heel if I have stirrups, but cargo shorts/pants, bike shorts, and jeans have all made appearances in the saddle, and occasionally I just cross my stirrups and wear my non-heeled muck boots for a quick flat. Even if I am in boots, I also often skip the half chaps if I’m short on time and won’t be doing anything particularly strenuous; it all adds up.
Finally, it helps a lot to be there when nobody else is and to pick your times: if they’re in 12/out 12, for instance, and the “out 12” is in a 70-acre field, it helps a lot if you can get there after they come in or before they go out.