Sorry for taking so long to respond. The cooldown time depends on the thickness of the nylon filament, and possibly also the compactness of the coils. The thin (I'm guessing 380 um) filament that I was working with at first returned to its original configuration within a few seconds after being heated, if I remember correctly. I'm working with some 711 um filament now, in a tighter coil, and it takes quite a while to relax after heating -- 10 seconds or more. I'll try to do some better characterizations and supply actual measurements later, but I haven't had much time to work on the project this week.