I've done plenty of multi state / thousnad(s) of mile trips, and never found any issue with fueling taking longer than the other members having the potty break.
one person starts fueling while the other heads to the head, then trade off.. whoever is free, grabs food.
If anything might add a minute or two.. what's a minute or two in 40 hours of driving?
I've BTDT trying to skate thru a state on that last 1/4 tank of fuel knowing I have enough to make it thru, then poof.. the 3 hour traffic jamb starts and you are sweating bullets.. or that service station you normally stop at AND the next 4 exits are closed due to the recent hurricane ( BTDT in lousiana ).. or you pull into town and the all night truck stop is OUT of diesel, and the next station 2m down the road closes at 2am, and it's 2:15 already, thus you have to wait, pulled over till the station gets fuel at 7am, or the next one opens.
Periodic stops also let you do things like look at tires, hubs tie downs, cargo.. etc.. etc.
I'am all for iron man-ing it.. but sometimes it's worth it to stop, if for other than comfort reasons.
every situation is different mind you.. i don't drive out of state for 'vacations'.. if I am more than 2 hours from my house, i'm pulling a trailer and there is likely a tractor involved.. or other large cargo coming or going.
My f450 has an aux 50 gallon auto xfer tank in the bed, and when I leave on a long haul, i STILL carry 4 5g cans of diesel with me, plus a gas can, if it involves a gas tractor.. plus a full load of tools, small air tank and compressor, 2-3x the number of tie downs I may need, winch, extra battery, electric repair kit, tire repair kit, spares for anything touching the road, extra jacks and cribbing.. etc..e tc.
noting like being 1200m from home on a rainy sunday, holiday night and need something ya don't have
soundguy