Works on some websites but not on others. Like the browser version of skype has no problem detecting the system time on my machine (even with a vpn on)

Uhm, Browserleaks.com still sees real system time via js toLocaleFormat and on browserspy.dk there is some additional info about date and time I not completely understand.
If this add-on doesn't mask all js date/time API then what's the point of using it?!