I am highly skeptical of carbon offsets.
They remind me of the cynic's definition of "foreign aid," which is "The transfer of wealth from poor people in rich countries to rich people in poor countries."
I was part of a Permaculture co-op. I am convinced we were a net carbon sink. We made alternative fuel. We planted lots of trees. Our agriculture was almost completely based on manual labour, not mechanization (the only exception was hay.)
Do you know how hard it is for a small (~$150,000 gross revenue) co-op to get carbon credits? I spent way too much time pursuing this, through elected officials and government agencies, to non-governmental organizations, and I even tried direct appeals to CO2 producers. No one wanted to so much as discuss it with us!
In our case, the benefits would have been immediate. You give us money, we'd use it to plant trees! We produced several hundred Paulownia tomentosa seedlings each year — it is the fastest growing tree in the world, and sequesters carbon at a furious rate! Plus, it's drop-dead gorgeous!
So, at present, it seems that "carbon credit" are basically a way for corporations to enrich themselves. And what do they do with that money? They spend it — which inevitably puts more carbon in the atmosphere!
So, to more directly answer your question rather than simply rant, I think the so-called "benefits" of carbon offsets are simply a way of legitimizing carbon emissions, while letting those who don't like carbon emissions to somehow feel good about them.
For carbon offsets to really work would require a fixed number of offsets that steadily decline over time. If carbon emitters — down to you, gentle reader, as you drive to work — had a fixed amount of carbon they could emit, then "buying" offsets would still result in declining emissions over time.
But the current state of carbon offsets doesn't work like that. There is no cap. Governments have swallowed the Adam Smith Kool Aid, and allow any amount of carbon to be emitted, hoping that higher costs will eventually throttle it.
In reality (as we are now seeing in mid-2022), higher carbon costs simply results in general inflation, as fossil sunlight is the master resource by which modern civilization exists.
I don't see people driving less; they're just bitching more! And lobbying their bosses for higher pay to cover the higher cost of commuting, on, and on, and on… until something snaps.