I don't use oak very much, probably more with meads than with beers. I like Hungarian medium and medium-plus toasts. I do it to taste. How fast the flavor develops is based on how much you use (total surface area) and how long it is in (contact time), as well as the age and condition of the wood. No firm rules, but I like to go slow with it.
As far as the flavor aging out, the oak flavor is fairly persistent but the tannins can smooth and mellow with time. It can take years, though. Think big red wines, like from Bordeaux. I think the beer flavors tend to fade first, so unless you go super-big with the beer, I'd avoid over-shooting on the oak.
It's a tough thing to match, but I think if you can assess how long it will be before the base beer peaks, then you have an idea of the level of oak to apply. Sometimes I'll make big beers overly bitter on purpose, with the intent that they will come into balance in 2-3 years, for instance. Remember that if you think the oak character is insufficient, you can always add more later.
If you go too far, you might try fining the beer with something that attracts tannins, like Polyclar, and see if that helps.