Here's the truth........practicing on a 7' table is better than not practicing so get the table. But do not believe or listen to the phooey about your skills improvement immediately transfer and instantly 100% manifest itself in your 9' table play/performance. Your practiced distance control and position play of the cue ball involves longer distances on a 9' table and cue ball energy becomes a lot more delicate. And then there's safety play on a 9' table vs. 7' which obviously involves harder shots.
But your skills will improve by practicing on a 7' table at home and with tightened pockets, that helps a lot. You just need to allow for rehearsing and practice on a 9' table at the pool hall where you play. Eventually, your transition/warm-up time will gradually reduce and your practice at home will focus on aspects of your last match that need improvement.....cut shot, banks, combo's, draw shots, stop, center ball, frozen rail, etc.
So you'll derive enormous benefits from having a 7' table instead of anguishing over not practicing or enduring some unbearable conditions at the pool hall. But it will never be as satisfying or beneficial as having a 9' table at home.....that's just the hard cold facts......so just suck it up and live with a 7' Diamond table at home and make the pockets 4 & 3/8" wide.......Oh woe is me..........If that's hard to live with, then you be crying crocodile tears.........Really now...... a 7' Diamond table is so terrible to settle upon????????
Fortunately I live in California and all of the pool halls went smoke free years ago. Now it's just loud music that's replaced smoke so I can tolerate that easily.....especially, when I like most of the music being played.