By the 10th day, the grafts are rooted. You should start working out the scabs by the 10th day. It may take a day or two to do this. You must make sure this is done as the dried blood sticks to the growing follicles in a stronger bond than to your scalp. Grafts may grow a little before they start falling out, which usually starts about the 14th day. So as they grow, the blood glues them down and could rip them out of your scalp. So by the 14th day, you should be able to safely apply minoxidil. I've read reports min helps with rebounding from the ugly duckling stage which is a brutal 2-4 or 6 months. But as you can tell, it is hard to have clinical studies on the benefits of minoxidil immediately after hair transplant surgery; too many variables.
For me, I did all of the above. Started applying minoxidil in the 2nd week to all areas on the top of my head. I started climbing out of the ugly duckling stage after 8 weeks. Had full coverage by the 4th month. Either I am an early grower, or minoxidil definitely helped me. It certainly didn't hurt any of my natural hair or even grafted hair.