I want to start a rock band in my spare time. How ...

Depends on the qualtity of music you want to make and to what extend you are already skilled - like every acticity practice is needed. I would say in general when i need to learn some new songs/techniques it is better to practice every day around 20 minutes and once a week the full picture, but also 2 -3 times a week an hour would work

To me, if you're really serious about something, you must dedicate yourself to it.

If this is just going to be a pastime or hobby for you, then practice in your spare time. Do what you feel.

If you are going to dedicate yourself, you should "live" in your music, so to speak. There shouldnt necessarily be a strict and rigid regimine for practice. Practice increases your skills and abilities. Dont just go through the motions. Its about challenging yourself, and honing your skills.

You should know when you need practice.Its all about what you really want, and expect from yourself, and your music.

I am not a professional musician, but have played guitar for 25 yrs. I'm proficient, but I always strive to better myself.

Practice as much as you can .

My opinion

All your spare time,  with everyone there, in all their spare time.  So it's going to be hard and take a long time.