I started with HP soaps, and I'm glad that i did it.
You can use the soap as soon as it is hard. But it should have a little dry down time. Your better off using a loaf mold with hot process soaps because it has the consistency of mashed potatoes. And even when it's done you still have a bar of soap that is softer than a cold process soaps. (this includes even when a bar has been sitting for months, it's still softer because of the process in which it was made.) So you also use it up faster than a bar of cold process soaps. The coloring is also darker with hot process soaps because of the heat applied during the process.
If none of those issues bother you then go ahead and do hot process soaps.
However you should consider learning hot to do RTCP soap. It's actually so much easier and nicer as well. This stands for room temperature cold process soap. Basically you mix up your lye and liquid solution and wait till it's absolutely room temp. I've even mixed it up several days ahead and used it days later. Then weigh out your oils and blend them with a stick blender while still room temp. I do suggest warming hard butters like cocoa butter separate just to make it easier to work with. Then pour in your lye liquid solution and blend with a stick blender. Once you have trace add in any fragrance oils or other additives you want to add, and pour into your molds. If your making a milk soap the coloring has a better chance of staying lighter depending on the fragrance oil being used. Some scents such as those that contain vanilla will darken the soap. I really like this process and find it a whole lot quicker and easier.
Once the loaf is hard or it's hardened in individual molds I've removed it and cut it. I've waited a couple of days before testing and found it a bit soft a day or two after it's made but it made a much nicer bar than hot process soaps. Then let the rest of the batch go through the rest of the dry down time to evaporate the rest of the liquids.
Anywho i just wanted to share some of my experiences with soap, and I highly recommend cold process soap even though it takes longer. Just because you have a nicer bar of soap, and it's extremely simple when you do the RTCP soap.
I started RTCP about a month ago and I LOVE it! I get my oils ready at night and in the morning, all I do is mix my lye and place it in a cold water bath until it cools...and thats it! I'm ready to go!
There are some really goood threads with info about RTCP in the forum if You are interested.