It depends a lot on how you administer the harmalas.

If you take 20mg sublingually before vaping, it could add an extra 10-15 min to the afterglow and slow down the experience into something less shocking and more manageable.

If you take 200mg orally then it could extend it up to 45 min or so.

Changa, you can just keep going until you find your sweet spot.

Everyone reacts a little differently, so you'll just have to do some experimentation to find what works best for you.

As far as dosing goes, this thread has a lot of the info you need.