Some background before I get to my actual question:
I was a full time poker player off and on from 2002-2010; I spent time in those years going to school and working on political campaigns but I would say at least 50% of the time, sometimes more, I was a full time poker player and about 75% of my income came from poker during those years. Since 2010 I have largely been focused on building a career beyond poker, first working with startups in the Los Angeles area and later working in politics again. Until this year I would say that I played less than 300 hours a year since 2010.

Late last year I decided to jump fully back into political consulting but in many ways I was a little late to the party for this years elections. The result of that has been lower quality clients than I had hoped for and the result of that has been choosing between chasing third tier clients in a rather unforgiving business, go hunting for a more traditional job, or go back to poker. I have largely decided on a combo of choices 1 and 2 because barring an AMAZING job offer the idea of going back to working primarily for other people just isn't appealing to me in this phase of my life.

With all of that said, I am definitely playing on a short-ish bankroll, I have about 3 months of savings behind me, and limited income incoming (about 55% of my monthly nut is covered by passive income as long as I live semi frugally- something I am terrible at.)

When I started playing again earlier this year I was playing sessions of 2 to 3 hours almost daily, playing very tight ABC poker. What I found was that this was leading to sessions where I won a little or lost a lot, but I was just getting comfortable again. Now I am at the point where I am playing sessions of around 4 hours daily and have opened my game up more to my comfort level (this includes opening from late position more, 3betting more, and just generally trusting my post-flop skills more than I have been) Doing this has lead to a higher overall winrate but also much higher fluctuations in my day to day results (the losses have been a little bigger on average but the wins have been A LOT bigger.)

Here is the problem I am running into, using last nights session as an example. I wound up in for my second buy-in very early in the night (flopped middle set with a flush draw on board and wound up playing for stacks.) I got down to about 1/3 of my 2nd buy-in and went on a small heater and wound up back to just about even. I was three hours into my session and seriously thought about leaving. I decided to stay, got crushed in a couple of hands and wound up down about 1.5 buy-ins for the night. I found this really impacted me emotionally (to the extent that I am still thinking about it and writing this today.)

My issues are wanting to really balance playing the hours and maximizing my winrate with protecting my bankroll and my psyche. Also, I am noticing that playing on a short bankroll is impacting my emotional response to losses and trying to figure out how to better regulate that.

It is a good idea to set up a timer. You will control how much time you spend on slots. Yet, you will need to force yourself to stop.

Maybe move down a level, if available, and do two 4 hour sessions daily, with a break in between. Clock in and out like a regular job, and stop the mental accounting. The smallish bankroll is a legitimate concern, however finishing a session up or down is not.

I would also say that if you've been losing I would consider "booking a win" even though people on here look down on that. I find it helps emotionally stabilize me when I'm running bad.

According to your background, you're definitely an experienced player who doesn't need any advice from a recreational player like myself about how to play at the table.
But, since I'm a big proponent of proper bankroll management, even though I never played professionally, I always like to offer my opinion in this aspect.
That's obviously your problem and I think you know it.
Playing on a small bankroll negatively affects one's play, no matter their skill level.
If course, you sometimes don't want to wait forerver until you can put enough money on the side, that's understandable.
It doesn't seem to me that your hours are too much.
To the contrary, I don't think that that's the issue.
Gl