One of the lesser known tendencies of bakers, and especially fate-bound ponies with baking cutie marks, is time keeping. Leave something in the oven too long, it burns, or not long enough and you risk making ponies ill. So when five minutes had passed, they all pretty much felt it in their guts, and surfaced at around the same time, walking up the river bank enough so that they could at least keep their rear hooves on the ground, and their heads above water.