Impossible, Gotenks was able to wait for the last 5 minutes of the fusion and then stay as SS3 for 5 minutes, but going SS3 since the start still granted 5 minutes of fusion. If it was a time consumption thing, SS3 fusion should consume time 6 times faster than regular fusion (30 / 6 = 5) and waiting for the last 5 minutes would result into a fusion that lasts less than a minute.>>184558094
Welp, that's a lot of headcanon, stop claiming everything is a retcon when several explanations could make sense of these scenes.
First nobody said they can fuse instantly after defusing, Piccolo could have been talking about wait 30 minutes before keep practicing. Nothing states they can instantly fuse after defusing.
Second we don't know how long was Gogeta and Broly fight in-universe, or you forgot stuff like the last 5 minutes of Namek? As far we know the fight could have been 4 minutes long.
Third we don't know if just having a big power is enough to make the fusion shorter, the problem could have been the power boost, the act of multiplying fusion's base form, maybe the time is shortened when you surpass the SS2 barrier, otherwise even base Gogeta would be strong enough to last only 5 minutes (but again nobody knows how many minutes was he fighting)