You can’t hold it for five seconds? Well that’s why you’re doing it innit. You’re trying to hold it for five seconds at ‘full pressure’. Once you can do that you go to higher bounds, 10 seconds, 20 seconds, right the way up to five minutes or more. The point of kegels is to get that BC muscle (the muscle that stops piss) so strong you can EASILY hold back ejaculate the same way you would stop piss.
There are other benefits, like improved erections, increased sensitivity, ability to orgasm multiple number of times in the space of a minute, shooting ejaculate further distances, having a stronger ‘piss’ and being able to stop pissing at any moment. And maybe others I forget. (Edit: also fully body orgasms, and orgasms that last much, much longer than you would ever imagine.)
You can do it either erected or flaccid - doesn’t make a difference. Think about it. All you’re doing is training the muscle, like you would for example constantly kick in martial arts to make your leg muscle strong. You do 100 kicks just so you can do 10 no problem in a fight.
Hope this helps Ywanker and hopeful_gainer. If you have any questions I’ll get back to you here. :)