In all descriptions I've found of planned redosing schemes like 1/4 to 1/3 the dose of harmalas is consumed with additional DMT as the redose, anywhere from 45 minutes to 3 hours in.
What happens if pure harmine is used alone for the supplement?

To date all my work has been either rue tea or mixed harmaline/harmine, and I've tended to get long trips with visuals lasting until around the 7 to 8 hour mark. I'm going to work with pure harmine and harmine+THH now and by all accounts harmine based trips are shorter. These reports match clinical data showing the halflife of harmine to be the shortest of the three. So would redosing just with harmine right before the peak lengthen the trip back to the harmaline duration without need of a DMT redose?

I would think that redosing other than oral ROA would be ideal in this scenario. At the peak, most of the DMT is going to have exited the digestive tract and be in the bloodstream. The digestive tract will bind up a lot of the harmine and it will take around 30 minutes for a significant amount to enter the bloodstream in which time MAO throughout the body will be eating away at the DMT.