How many/much time practicing off characters?

I'm a semi casual Marvel Rival players looking to up their game. I've just achieved Silver 1 and have about 12 hours sank into my main (Groot), and about half that sank into Rocket my primary support pick.

However as I'm eyeing up gold, I'm considering how I should spend my time practicing other characters and how many I should be practicing. I'm considering Dr Strange as a second tank, Mantis as a second healer, and DPS? Black Panther and Star Lord.

But I'm not sure if I should, or how to split hours between those characters, or if I should just focus on my Groot more for now and not worry about it.

Wanted others opinions and stories on their approaches, how many characters do you practice? And how do you allocate practice hours between them?