system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If I throw a rock straight up into the air, for how long exactly does it stay at 0 mph before it falls down again?

Is it the same for any mass? 

This is a bit of a weird one, but somehow I **really** want to know this.
gpt
In practice it depends on how accurate your measurement of speed is.  That is, how many digits you are willing to consider.

Mathematically you can work it out pretty easily.  The answer is zero seconds.  The top of a parabola is one point only, it has no extent.