How often do you stop or how long before you have to stop?
Thats individual, but for me I only have to stop for perhaps on average 1/4 of a minute, it varies, depending on how horny I am or how attracted I am to the girl I'm with or how good the sex feels, how tired I am etc etc
If I'm really turned on and the sex is great, probably a minute or so, or if Im jerking off and particularly horny, around 1/2 a minute at a rough guess
Its up to you to discover these things, eventually you'll get to know your own body far better and be able to guage for yourself, it pays dividends when youre actually having sex with a partner
Dont expect instant results but if you stick with it, after a week or 2 you should really start to notice a big improvement in staying power and control in terms of delaying your orgasm