PDA Time and internet access

Hi
I have 2 issues around PDA
We use several ?Windows mobile devices? at work. Palm trio and some that are Rebadged ?Vodfone? .
They will all synchronize emails with no problems but on some of the PDA’s the diary function is 1 hr adrift. I have set the time on the PDA but when the diary syncs it is an our adrift.( This generally occurs when the diary entry is entered on the PDA) These PDA’s do not connect to the PC for Synchronization, they connect to the network wireless.
The other question is ,what is the best way to restrict the sites that the users can view on the PDA?.
Any help or advice would be greatly appreciated .