Depends on a lot of things.If going from a 2 cam/round wheel bow with a soft back wall to a solo cam with a solid back wall...it'll take longer than if you simply went from brand "A" solo cam to brand "B" solo cam (could be 2 cam bows as well...you get the idea).Double that if shooting a back tension release.
Also, it might take a while if you drastically change ATA or weight of the bow.
IF your not changeing too much (say going from a Mathews to an Alpine solo cam) you should be able to get on target pretty quickly (1 day or less)