Firstly, just edging as part of a session is great. As you’ll have seen I do recommend trying it for longer as you get the extra benefits of the ‘denial high’ and it’s a good challenge. But if you find that just edging in a session before you cum is what works best for you, that’s fab.
So, some ways to force yourself to hold off longer – a classic is to set a timer and just practise stopping as soon as it goes off, or, not being allowed to cum until it does, otherwise you ruin it
Another is starting edging when you know you only have a limited time. i.e. you’ve got to get to work or school or guests are due over. That’s can be fun!
Thirdly is try masturbating in ways that you CAN’T actually cum. Classically for many that’ll be penetrative sex or even just humping