Dawgmaster,
From your questions I will assume you are relatively new to F-Class shooting and I will approach this from that view point. I don't practice at all and only shoot 3-5 major matches a year, but I have 48 years of competitive trigger pulling in a large number of disciplines; the last 12 with F-Class. Even so, I have to really work the first day or two in a large tournament to remember everything I know and to retrain myself to do things without thinking about them.
A relatively new shooter should practice enough to develop mental and muscle memory to the point that a shot is fired without conscious thought of the event happening. You should be able to concentrate on the wind and mirage and how it will affect the bullet impact and not on your rifle holding or aiming. How much time or rounds fired depends on the person and how he practices. You should practice as you would in a match. Setup a routine and checklist for everything you do.
There should be goal to you practice sessions. Shoot against other shooters. Do not practice for practice sake. Bad practice habits are worse than no practice. The best practice is matches themselves. By shooting in matches you get to pick the brains of other BETTER competitors when not firing (i.e. in the pits). Doing so will increase your knowledge rapidly. Reading books on competitive shooting is another way of picking brains.
To improve you must have a goal for every time you shoot. It can be a personal best score or beating a certain better shooter for the first time, whatever, but you need a goal. Notice I have not given you a number of rounds you must fire or the number of barrels you need to burn out. That is for you to determine. Don't forget about dry firing. The "old geezer" J.J. Conway, the father of US F-Class shooting used to dry fire at home quite a bit.
You are the one who has to determine how much practice you need, but I will say this...COMPETING in matches are the best way to improve your scores.
Best of luck,
Larry Bartholome