I spend at least as much time on the green as range.
I like to alternate range practice / putting one day and short game / putting the next, splitting 50/50% each.
My green sessions are exclusively with one ball. Only get one on the course, why wouldn’t I practice that way? I see people dropping 2-3 sleeves, no idea what they’re accomplishing. I start with random, longish lag putts (40-60 ft), preferably up- and downhill, to get a feel for speed, break, grain, etc.
Next, I set up for 3-point drill (detailed on another post; briefly: set a tee 2’ behind hole, a start tee 20’-40’ from the hole and two dimes about midway. Read the putt, adjust the dimes a putter-width apart on the intended path. Hit putt. Point for gate, another point for ball finishing between cup and 2’ tee and 3rd point for make). I’ll reset everything and repeat, making note of a) misreads, b) distance control and c) start line errors.
If a hole is available, I’ll hit 2.5’, 5’, 7.5’ and 10’ putts on 8 compass points. If not, as @Dewsweeper says, I’ll find a vacant spot and throw down a ‘false’ cup (a dispos-all gasket). The 3-point and compass drills represent the bulk of my putting practice.
If possible, I’ll finish up with a zig-zag tour of vacant holes (20’+) where I try to two-putt max each.
I have an ankle issue so I can bear no more than 2 hour sessions, but I try to get in two practice sessions per week (plus 2 rounds played). Made me a helluva putter!
Hope this helps!