So question is, what is the threshold?
As suggested in above error, if we check web client logs, below entries can be found
So it clearly mentions that, current time does not fall in the request lifetime interval extended with clock tolerance of 600000 ms which would be 600 seconds or 10 minutes.
Similarly, we also have the time skew tolerance threshold between PSC nodes. This is also published by VMware in configuration maximums document as in screenshot below.
If you have vCenter Server as VM, make sure you use only one time sync method i.e. network based or with ESXi server. Try to use common time sync source like PDC emulator for your environment in AD.
So in short, we need to ensure that time sync between vCenter Server nodes is correct in order to avoid any issues.
I hope this helps!!!!