The harmalas should be completely out of your system by 12 hours.
I can't say definitively, but meclizine seems to work fairly well to counter the vertigo.
Due to drug interactions, I cannot partake but when I'm clean of all the reuptake inhibitors I plan on mixing harmine, DMT, meclizine, and lemon oil. Theoretically, this should result in a clean trip with no nausea, purge, or vertigo.