When I was working for a startup, and working from whatever time I woke up, till 3am in the morning, time flew by so quickly. I could easily do 80 hours, and have great fun. I was creative, and energised.
As soon as I went from a startup to working for a large employer and was forced to do 8.30am till 5.00pm all my productivity and energy flew right out the window.
Sigh.