The most disappointing: 5 seconds. These usually just sneak up on me during sex and aren't super pleasurable or fulfilling. Usually when I'm multitasking (sucking nipple, rubbing clit, supporting body on other hand)
The best: 20ish seconds. Long pleasurable buildup, ejaculations and muscle contractions are less sharp. Usually also comes with a lot of cum too. Brain ceases to function for a good minute or so as well.
I'm male if that isn't obvious.
This is far more interesting than the robot.