Not to worry, the studying you have already done for CCNA and CCNP SWITCH in the past does not go to waste. Much of the content is still valid for the current CCNP exams. For any CCNP certification, you first must pass the CCNP ENCOR 350-401 exam. So the best bet would be to begin going through that course, which is found at the following link:
You need to get that under your belt first before choosing any concentration exams. Once that’s done, you can go on to the ENARSI course, which is CCNP Enterprise, can be found at the following link:
Having up to four hours a day available for studying is excellent. It gives you a lot of time to focus and to zero in on the areas where you need to study most.
After that, if you want to focus on other areas, you can then choose any of the other concentration exams, all of which are listed at the following Cisco link:
So I suggest you go start by going through the ENCOR course, do the labs (labs, labs, and more labs!) and see how it goes. If you need help along the way, you know where to find us!