Aeroplane 12hrs, Hotel room 24hrs, aeroplane 12hrs
We do a variety of ops in business aviation and the above is the most tiring.
You arrive at your hotel having been on duty for 12 hours, awake for 15 and you are tired. Do you go to sleep for 8-9 hours and then fail to get any more rest for the 15-16 hours before your next 12 hours duty .... its difficult to manage and impacts on safety as you approach the highest work load period at the end of your next 12 hours strapped in to a jet.
12hrs aeroplanes, 12hrs hotel room, 12hrs aeroplane
This is actually easier (although much less fun), you get to the hotel, eat dinner, go to sleep, get up, eat breakfast and report for duty ... at least this is safer but very boring and not the shiny dream of working in a legacy.
Best of luck in the ensuing negotiations