I cannot come close to Bob's experience, but I don't mind telling you what I do.
I use a sponge to wet my lighter weight leathers if I have to do a quick job or last minute. If I have a heavier weight leather, I will follow something close to Bob's method. I don't use a box, but I will use a plastic bag and just set it on my granite block overnight. I have also used the method of dunking my leather and then setting on my block with a piece of glass on top to set up overnight. Both methods have work well. I guess it just depends on my mood. Oh, my water also has Pro-Carve in it.
The thing that you need to look for that is more important is how your leather feels. For instance, is it cool to the touch? How does it feel when you place the grain side up to your cheek? Cool/cold is good, hot or normal would signify that the moisture is gone. The color is another factor, but you can not depend on it because of the different leathers. I have used Tandy leather, which is bleached and the color is different. Hermann Oak leather which is what I use now shows a different color when wet and dry. I can judge by the color in HO, but not Tandy.
Now, I have found that lighter leather will dry out faster than thicker leather. If my lighter leather appears to be dry, I will turn it over and wet the back. I will then keep it that way on my granite block and allow it to set in for about 15-30 mins until it absorbs it. The time is not crucial, you can check it to make sure it sets in and is ready. You can always leave it longer depending on how it cuts or tools. Play with it.
Remember, I am a hobbyist and do not do this everyday like others. Maybe someone else will chime in to help you.
Good luck