I pump up my tire to a target pressure, measured using the gauge on my floor pump (> 15 years old, I've no idea how accurate the gauge is), and based on past experience with the particular tire I'm running, and also dependent on my ride (slow/fast, good roads/not-so-great roads, wet roads/dry roads, etc.). So, for a "fast" (for me) ride on decent roads that may be a little wet, just as an example, I might target 65-ish psi in my 32mm tires (rear), and a couple of psi lower for the front. Probably a little below 65 psi, actually, I'd just eyeball it as I got close to 65 and stop pumping when it felt right.
Then I pinch the tires between my finger and thumb, look up at the ceiling for a couple of seconds, and maybe add a little air or let a little out depending on my gut feel.
Then I ride.
Takes about a minute for both tires. Maybe two, if I haven't ridden in a few days and the tires are low.
After my ride, if the feel was overly harsh or overly squishy, then I keep that in mind for next time. Or, maybe I forget and make the same mistake again, but eventually the feedback influences the actions resulting from the pinch test (which is really the gold standard - the gauge just tells me when I'm getting close).