Same symptoms here on my Foxsat HDR with custom firmware:
Recording BTCC on ITV4 was due to start at 10:45, but from the box's perspective it started at 11:43
The guide is showing GMT +2
I was recording at 3am GMT, though I do have a separate wake-up set in the menus for 4:30 every day.
I suspect channels with Accurate Record (if you use Auto for timings) may be OK, though I'm not sure how long the box will wait for a start trigger before giving up - BTCC was less than 1 hour as the programme started 2 mins early.
Running custom firmware 4.1.1. Will investigate in a bit more depth at some point, but not now as currently recording the touring cars.
(It's also worth saying at this point - I have complete appreciation for all the fantastic hard work that everyone involved has put in to the Custom Firmware project, and regardless if this issue is somehow related that of course does not change my view at all.)