I do both. I have a set amount of time thats planned, but I try and keep count as I go. If I finish my set number of reps and still have alot of time left, then I know I rushed them to much.
I usually count in sets between 10 and 25, just depends on how I'm jelqing.
This keeps me going and I can get a good idea of how many total jelqs I've done for the day...
I used to rep, but I'd zone out and lose count of my reps and it would drive me crazy. I'd be on 143 and forget so just round down and go to what I last remembered which would be like 110.. Easy way to overtrain.
I do both. I have a set amount of time thats planned, but I try and keep count as I go. If I finish my set number of reps and still have alot of time left, then I know I rushed them to much.
My opinion- count reps instead of going by the clock. My reasoning behind that is that counting reps gives you more precision (for adjusting volume), and the act of counting itself is conducive to maintaining a good tempo.