Just a side note - my youngest son was a wanderer...he would be so caught up in what he was doing (riding his bike, trying to catch a toad, collecting things) that he would just follow what he was after and not pay attention to the fact that he had left his "boundary area"
That was his most frequent reason for time out....we talked a lot about what he could do the next time, like ask me or his older brother to go with him. I also talked to him about how it made me feel when I couldn't find him (he was literally the kind of kid who could be there one second and gone in the blink of an eye).

just an example of how I used time out....before, during, and after.

Also, I agree with the one minute per year of age, but with this situation - maybe starting at 3 minutes instead of 5 and gradually increasing.