In Iron distance events, you can actually have a little sit down and rest in transition
Because you’re racing for 12ish hours, shaving a few mins off in transition isn’t as important
Also, when you’re going to spend 7 or 8 hours on the bike, you want to be wearing proper padded cycling shorts and socks, rather than a tri suit which just has a nominal bit of padding around the bum
So for those events, people will take a few mins to change kit (within the strict ‘no nudity in transition zone’ rule so putting shorts over the tri suits rather than a full costume change!) rather than the few seconds that people aim for in short course events
To eat, you have a pouch attached to the cross bar of the bike with gels, snacks etc - it’s called a bento! Plus 2 water bottles
And yes, if you need a wee, you do it while moving. Standing up a bit in your saddle is usual for women
For really long races, there will be nutrition on the course as well. Less so in sprint races
Also less need to relieve yourself