kaba have you found out what the problem was? I have the same issue, i can't get the time write on one of my Celerra simulators. I have tried on the same way, also thru the web interface, but that also doesn't work. ps i only have a difference of 1 hour.
I did find out that my esx hosts had incorrect time between bios and extenal NTP. so I had to syncronize it first to make sure that all DCs are getting correct time. therefore PC that had simulator also has correct time. I have to reinstall the simulator so can't really tell yet if it corrected the issue or not.
Time sync doesn't work here either. The Data Mover seems to stay in sync, but the Control Station gains time at an unbelievable rate. No matter what I do to the ntp.conf file, it won't synchronise to any servers (two local Cisco routers and one *.pool.ntp.org).
However, if I re-start the ntpd service, it quite happily corrects the time.
The VMware site goes on about various problems affecting clocks in VMs, but I didn't see anything that made any difference.
My only workable solution (a nice dirty hack, but it's only a simulator ) is to add an entry to crontab to restart the ntpd service every 5 minutes. It's not perfect, but at least the CIFS checkpoint times appear OK in Windows.