One useful thing, is to keep the extender - when pushed back/compressed - so short ( pardon the expression), that you have your glans almost in front of the extender.( of course you’ll have to pull your penis outwards)
Then fasten the tube or strap, and release the device and feel/see the stretch on those markings. If there’s little stretch adjust the screws to preferred stretch.
If you put together the extender as a too long device for your penis,
Your glands is going to be under much stress, and pain as result. The tube or strap has to be pulling downwards instead of forward «through» your glands.
This should help you to manage more hours. I know its fun to put together a long/too long extender to impress yourself, but it will be painful and you might not manage to be there for the long run.