A few weeks ago actually. I did UA, LAX-SFO-SIN-SFO-LAX. I left 8pm on a Monday, and landed back in LA at 12 noon Wednesday.
I worked and ate the first 1.5 hours of the flight from SFO-SIN, slept for 8 full hours and woke up with 7.5 hours to go. Thats when it hit me how long that flight truly is.
Tons of fun, can't wait to do a few more international quick-turns this year!