Ask HN: Rough timelines to issue PIPs, and terminations

This isn't a problem I'm currently dealing with, but I've recently noticed that there doesn't seem to be strong mental models around this particular problem... so I'm curious:

What timelines do you use or recommend to put an individual on a personal improvement program? (allowed time for ramp up, timeline after letting them know about poor performance)

What timelines do you use for termination after or during a PIP?