From the player's perspective, zero checks would be optimal since automatic success is better than leaving your fate to a d20. Per the rules, there are three tasks to perform - finding it, figuring out how it works, and then disabling it. If the player can remove the uncertainty as to the outcome and/or the meaningful consequence for failure from a task, then there is no check. So in practice, there could be anywhere from 0 to 3 checks.That is alot. I say two at best would be optimal.