If I dose dmt 20 minutes after the maoi, I find the experience to be relatively short, from 60-90 minutes. But If I take dmt orally 90 minutes into it, the experience lasts for many hours. I think it may depend on the amount of maoi you take. This was with relatively low amounts of dmt. I believe if you dose higher amounts of maoi, your experience will be much longer if taken at the same time. This may be because with relatively low amounts of maoi in your system, the dmt is broken down quickly. But after an hour, there should be more maoi in the bloodstream, causing the dmt to last longer.
For instance, if I take 100 mg of harmine, then if the dmt is taken at the same time, the experience should be relatively short, 1-2 hours. If I wait 60-90 minutes, the experience would be more like 4-6 hours. With 300 mg of harmine, the length of the experience would probably be very different.
Basically, the lower amounts of maoi you take, the shorter the duration of the trip. If you adjust the amount of dmt upward in combination with low amounts of maoi, you can get a strong and relatively short trip.