WOJ was that Harry already spends about a full time job's worth out of an average week in his life on maintenance and improvement of foci.
I recall it being closer to a part time job. Around 20 hours a week. That's still a huge amount. There are a few things that might change that though. First, Harry is better at it than he used to be. In
Changes, Harry said each time he re-upped the enchantment on his coat, it lasted longer and he thought he had figured out how to make it last almost a year, up from six months, if I recall correctly. Second, early in the books, Harry talks about "full enchantments" that don't wear off. They are expensive. Harry has resources now he never anticipated. Maybe if money isn't an issue, he can do full enchantments (which he does describe as time consuming, so maybe it wouldn't help). Third, Harry doesn't need an income anymore. Still, I agree with your premise that it would probably take more time than Harry would be willing to sacrifice. He'd probably find other pursuits more valuable. Like maybe carrying out full enchantments so he could eventually have the time.
Speaking of cool things Harry's money might be able to do for him gear wise, in
Fool Moon, Bob and Harry have the following conversation:
Bob: I'm talking a greater Ring of Invisibility, not just a Shadowcape or something.
Harry: Do I look like I'm made of money? I can't afford that.
I hope Harry gets some cool gear he couldn't have afforded before he had a bunch of diamonds he didn't technically steal from a god.