Depends on your recipe & your process. As soon as it is set up enough to remove from the mold, I let it sit out to rest a few minutes or hours (as I said, it depends on the formula and your process.) Are you talking about CP or HP soap? Did it go into the mold very fluid or very thick? Did the soap heat up fast? Did it gel or not gel? What kind of mold are you using?
Did you use a low or high or mid-range lye concentration or water to lye ratio? (That's part of your formula, by the way.)
All these things impact the correct answer.
With a gloved finger, check to see if it feels like pressing on a block of cheddar cheese. If so, it is good to cut.
Some examples: A 100% Coconut oil soap can be ready to cut in a couple of hours. A 100% plain olive oil soap (not pomace) can take as long as a week to set up sufficiently to unmold and cut.