Time is set by the cell towers.
Been that way since the Pleistocene.
That being said, I wonder if the clock is also set by NNTP over the WIFI? This capability was added to Honeycomb/ICS for tablets.
Your you turned off the check boxes for "USE Network provided Time" I could see you having some clock drift.
If the HOX is getting time from your router, and your is not synced with a time server, that could cause drift as well.
This has got me thinking. My HOX drops wifi every night at midnight (or within a few minutes thereof). I'm wondering about where it gets its time now. Maybe my router is horked.