Interesting… I think Fly.io’s new Sprites are intended to be their main answer in that niche, although they’re fairly early in development. (Forking is still on the to-do list, for example.)
The docs for them have timing expectations for the existing snapshot and rollback operations, and those at least sound more in line with what you were looking for:
Checkpoints are live and fast. Creating one takes about 300ms
Restores are fast—typically completing in under a second
(Although, I would have expected the traditional platform’s volume forking to be much quicker in reaching the hydrating state, to be honest. Maybe an early onset of the current management plane outage was slowing that down. Sometimes problems gradually build for a while before the actual meltdown…)