[...] how many days/sessions/hours per week is the minimum amount most of you feel is realistically needed to maintain, and how many more is needed to improve?
I think most players can improve with as little as 10-12 hours per week. This plan assumes you have a table at home.
You CAN play productively by yourself, and there is an advantage to doing that for time-limited players. Think about it. If you hit ALL the shots rather than half the shots, you shoot in one hour by yourself as many shots as you shoot in two hours against competition.
Though I know a lot of people find value in them, I am not generally a big fan of drills and repetitive shots.
Also, imo, most people will realize more benefit from shooting the easy shots a little better that they will from shooting the hard shots a little better. But practicing the easy shots is difficult because there is not a good feedback mechanism. Because you succeed most of the time there is not much corrective learning going on. Practicing that long tough cut down the rail SEEMS like good practice because you're getting lots of feed back and perhaps can see some progress, but, once again, I don't think it is the best practice, particularly for a time-limited person.
Most of us make the same errors over and over again. We overcut or undercut the same shots. We come up short with the cueball on the same sorts of shots. We get a little too straight or not straight enough on the same sorts of shots, and so forth. So when practicing it is important to develop a TRAINING MEMORY---when you overcut a ball or come up a little short or think after a shot maybe you should have gone one rail rather than two, make a brief little mental note of it and move on....
So what is the plan?
Take an hour every morning (or whenever) and do the exact same thing. This accounts for 7 of the 10-12 hours. The first rack is warmup. Bust open the 15 balls and hit them all in being sure to let out your stroke a couple times. Not two racks; not half a rack; exactly one rack.
For the next 50 minutes or so, do Equal Offense (EO). Modest open break of a 15-ball rack, spotting any balls that go in. Start each inning with ball in hand behind the headstring. Run balls like in straight pool. Though the maximum score for an inning is 20, keep going until you miss. You will probably get through about 10-12 innings a day. EO is scored by adding up 10 innings, so the maximum score is 200. Don't worry about how many innings you do, you are just keeping a running score, like this
Monday 10
Monday 2
Monday 0
Monday 6
Monday 14
Monday 7
Monday 19
Monday 5
Monday 20 (23)
Monday 10 --- 93
Monday 7 --- 90
Tuesday 11 --- 99
Tuesday 5 ---104
Tuesday 9 ---107
Tuesday 14 ---107
Tuesday 0 ---100
Tuesday 16 ---97
...
So everytime you score an inning you are adding a new score (16 for the last inning) and taking away an inning score from 10 innings ago (19 for the last one). So your total went down by 3.
Plotting these totals versus time you will see a lot of scatter, but if there is improvement over the course of months or a year you will see it.
Every inning you do, you know from the start what score you are dropping off your total. So you know what is possible. For instance, the next inning will be dropping off a 5, and so if you score 20 your new total will be 15 more than 97, i.e., 113. That would be a new record.
You will be amazed how much this matters to you, and you will be amazed how much you start paying attention to the little things and how much better you get at those little 3-ball patterns near the bottom rail. And you will be amazed how bummed you get when you miss your first shot--knowing that ZERO will be on your back for 10 innings....
The other 3-5 hours? A competition session with someone at your speed or up to about 50 points better. The key is not so much learning from that person as it is that person being able to capitalize to the right degree on your mistakes. You missing a safety versus getting a modest hook should matter. You getting a modest hook versus a better hook should matter. If you play too good a player who can kick to the right side of the ball from either of your safeties, that doesn't help you much. Plus you shoot less.