I’ve seen this movie before. Based on a true story.

I have to wonder, if Sweetie Belle had urinated, say, two hours after the lift had broken down, would it have started immediately afterward, or would they have to wait another six hours for it to start working again?

When the machine is broken, it’s been all day for the cutie mark crusaders and Sweetie Belle can’t hold it any longer till she accidentally pee since the water keeps running.

If I was doing a comic like this I would only make two changes to make this part more realistic and more in character.  
I. When Sweetie Bello “goes” I would put the words “21 seconds later” somewhere above the “hnnn…”  
since (according to a recent video on the SciShow YouTube channel) mammals (including dogs and humans (and presumably ponies)) take 21 seconds to empty their bladders.  
II. I would have Sweetie Belle say, “Oh, Come On!!!” instead of, “You’ve got to be … kidding me”! I don’t think I could picture Sweetie Belle using that type of language under any circumstances. Apple Bloom and Scootaloo, on the other hand, may be another story…

@Background Pony #D165  
Also, Sweetie Belle probably forgot how to pee standing up after being toilet trained for six to seven years, and so when she finally went she did it sitting down like she would on the toilet.
 
Also, I would imagine that when she uses the toilet she closes her eyes and pictures a bathtub faucet running full force just like she does here. It makes sense to me because her wetting seems to be at least semi-deliberate. I can’t really blame her for doing it, though due to the time that she has been this desperate, along with her obvious level of discomfort.

I imagine Scootaloo would be the most comfortable up there if she weren’t sitting next to Apple Bloom, who looks like she’s on the verge of a panic attack. And, poor Sweetie Belle’s being encouraged to urinate over the edge of the lift, in spite of really not having enough room to maneuver around. And then, the ski lift only starts moving again after she’s emptied her bladder, which she apparently had to do sitting down.

That’s ok Sweetie Belle. Nopony can hold it  
forever.