And there is the daily "working time" limit of 10h per day.
An unofficial calculation of the German CAA would be like this:
10h working time minus 15min "pre flight check" minus 30min "after last flight check" minus 5 min Start up (Block time) minus 5 min "shut down" (Block time ) would leave you with the maximum of 9h 05min flight time per day.
This time of 9h 05min would include the refuelling of the ship, so guess your realistic flight time per day.