This has to be the most unusable wincon ever
Even if Sans has Hypersonic Attack speed his MOVEMENT speed is complete
He would have to stop time and physically walk 4KM to reach Buu
Something which he likely could not do to possessing Average Stamina. I mean the guy showed to be tired in his fight against frisk(chara) and that no doubt lasted less than an hour and now your gonna ask him to make a 4KM walk to reach Buu?
There’s no definite answer to how long he can even have time stopped for. I’m all those scans he barely has time stopped for a solid 5 mins and again he has Average stamina that that doesn’t do him any favors either.
To say he can stop time long enough to waltz all the way over to Buu at a
snails pace and
stamina before the planet gets nuked when their is no definitive evidence he can even have time stopped for any longer than an hour seems like a massive and implausible stretch to squeeze a possible wincon in this situation