Learn to keep stroking
Don't stop, keep going at your speed. That speed you are stroking now is the standby stroking speed, because you can stroke like that for hours without cumming. See that wasn't so hard, was it?
The problem is you are stroking pretty slow, and it is not much fun to watch that. So we are going to increase the speed now. I want you to increase the speed slowly over the next minute, and then decrease it the minute after to your standby speed.
It should feel like a wave of arousal, you should get more and more aroused while you increase your speed, and cool down while you decrease it slowly. You shouldn't be able to come near the edge when you increase the speed, i said go slow. I don't want you to wank like a maniac after one minute, it should still be slow and gentle, but arousing enough to make a difference to the standby speed.
When you are back at the standby speed, i want you to do it again, one minute building up speed, one minute slowing down. When you have done this two times total, keep up the standby speed and ...