I’m lucky in that my job doesn’t require me to produce known results on any particular schedule. That gives me the fantastic freedom to work on these kind of problems during the evenings until I feel I can walk away from it, and then turn around and work on personal stuff during business hours. There are some short tasks I occasionally have to focus on right away, but that’s like a 1 or 2 day task, then I’m back into the relaxed schedule again.

Unfortunately, like OP, I too get deep into an interesting problem and then I can’t turn it off. “Oh I’ll just add this quick line of code” and two hours later it’s time for bed. What I HAVE managed to accomplish over many years is finding a stopping place where I can let it all go, and then drop it until I get back in the office again. I have to do that with personal projects or research too because I’m always working on something new that captures my attention and it really tends to put a halt on casual conversation. “That’s cool about last night’s game, but have you heard about this theory of a hydrogen haze obscuring the view of the early universe for the first few hundred million years? Well, I don’t know shit about sports, so now you guys know how I feel.” 😀