I knew I should've been more specific. The 2.5 hours and a sector only counts if it's self drive.
If you're sat in the back of a limo our allowable FDP starts at the report time and all time (no limit) spent positioning counts as duty but it doesn't count as a sector for FDP purposes.
It's never happened to me at this airline but I assume they'd treat it as a normal delay and utilise up to max FDP.