We left Amangalla at around 9:00 p.m. and reached CMB at 01:00 a.m. for our flight to DXB (dep. 03:00 a.m.).
The driver (not from an Amanresort but a contract company) had picked us up at Amanwella at 4:00 p.m. and after our stop in Galle he became somewhat tired and agitated just before midnight which wasn't very relaxing for us. After I offered him to stop and take a break he suddenly was back in shape...
If you get an afternoon dep to MLE you can take the car to CMB in the morning after a good nights sleep and breakfast but I would try to catch an afternoon flight with the water taxi to CMB for an evening dep. to MLE.
When arriving in Sri Lanka on a longhaul redeye I would recommend to take the seaplane as with a limo an already long journey could feel like it would never end.