Night Hours?

Regardless of what time you start work, if you do any work between 00:00 to 04:00 you’re classed as a night worker and restricted to 10 hours working time in any 24 hour period.
(As has been said the 10 hours working time limit can be opted out of with a workforce agreement)

Be aware that the period of 24 hours is actually 24 hours and is not reset after a daily rest period the way it is in the drivers tachograph regulations.
If you start at 03:00 and there is not a workforce agreement in place then legally you can only do 10 hours working time by 03:00 the following day.