Some things are worth taking a day off for.
The effects are so wildly varied that I don't think anyone could say... People can sometimes have such powerful experiences on the stuff that they've got to devote quite some time to processing everything and learning new ways of being and living; it's more a matter of you, where you are in your life and how you approach it in those instances than your dosage in particular.
Iboga isn't something a lot of people are capable of taking lightly, and with any psychedelic it can often be beneficial to take some time to yourself to accept and understand the very personal and powerful lessons there are to learn.
That being said, provided you drink it on Saturday have anything resembling a "normal" metabolism, you should only have very slight troublesome effects by Monday if any (slight sensory distortion, tracers, altered headspace and distracted thoughts, etc). A gram would have some people, including myself, in a significantly altered state for multiple days though... Rules of thumb are hardly applicable in some cases.
Variables in tolerance, plant potency and preparation/administration are considerable.
Physically, you should be just fine to work and participate in society at large. The rest is up to you and whatever fate there may be.