An article describes clock skew attack possibilities §§:
These can be attacked by repeatedly connecting to the hidden service, causing its CPU load, hence temperature, to increase and so change the clockskew. Then the attacker requests timestamps from all candidate servers and finds the one demonstrating the expected clockskew pattern.
If a server does not use time synchronization services like NTP etc, is it still vulnerable to clockskew attacks?
To be clear, the server only has a local clock and time is kept up-to-date by an administrator manually updating the system clock at random times, as and when it's needed.