Complex question about possible UK Compo for a delayed flight. Any help or advice appreciated please.

I booked a flight from LHR to BKK with Malaysia for 14.08.2024 leaving 11am for KUL. This flight was badly delayed and estimated to depart at 6pm.
I visited the MA counter when it opened for the night flight the night before (13.08.2024). The lady gave me the option to fly the same night instead so I took it and arrived early.
The lady at the check-in counter said I could claim compo for the delay even if I was early.....It did cause extra costs and I lost my hotel room in London for that night and an extra night and taxi at BKK etc.
Advice please.