My suspicion is that this convention is strongly linked to the practice of ingesting capsules of powdered rue seeds. Because the dissolution of the capsules and the digestion of the rue seed takes some time, a delay before ingesting mimosa tea would be necessary in order to prevent the breakdown od dmt by the body's mao enzymes.
However, when ingesting rue tea, concentrate or purified extracts, these delays usually do more harm than good. Free harmala alkaloids are taken up very rapidly, much more rapidly than dmt I believe. Indeed when not actually ingesting encapsulated rue seeds, it is best to always let the harmala solution accompany the dmt soltution, just like in traditional brews. The same applies when ingesting encapsulated pure dmt with pure harmalas, together they must go.
For the paranoid who worry about ensuring optimum mao inhibition, a pre-dose of rue alkaloids at T - 15 minutes can optionally be employed before ingesting the actual workload cocktail of maoi and dmt.
The ingestion of raw rue seeds seems to be a relic of ancient lore from days gone by a long time ago. Archaic practice that is unfortunately still being disseminated by sites like erowid. Last time I looked at that site for information on growing peyotes, I was surprised and appalled that most useful info presented on that topic was more than 20 years old.