From memory these cars do 40 to 45 minutes per stint in real life. We ran about 47 minutes when we raced at the Glen and we definitely needed a splash/dash for that but I think I opted not to change tyres to try to save a couple of seconds.
Remember in AC tyres are changed at the same time as refuelling so for anything more than 15 or 20 litres you might as well change your tyres too.
I voted for 60 minutes but I'm not bothered either way
40 would be perfect for a sprint race while 60 would force a fuel stop (+tyres) but doesn't really add much degree of strategy to the racing. Maybe a mix of both? 50 minutes is neither here nor there.
Now if we were to race for 3 hours at say Daytona, then strategy might come into play