I am running solaris 8 on an ultra 10...
Every so often it has an issue with the time...
The time seems to stop - ie. when I issue the date command the time is not changing... therefore anything in cron doesnt run.
When I set the date again - its fine for a few weeks and then it pauses again. Iam not using ntp - any ideas ?
Seems ur batteries need to be changed 
Sorry? Its an ultra 10 - is there some cache batteries or clock battery that could be faulty?
Anyway of knowing this for sure?
Yes, an Ultra 10 has a lithium battery in it. I believe it is used to power the system clock and NVRAM. When the clock locks up check if your NVRAM settings are cleared or returned to defaults since that might be happening too if the battery is dying.
Here is a link to the Ultra 10 service manual. Section 8.2 has instructions for replacing the NVRAM/TOD module, which I believe (but not positive) is where that battery is located.