Believe it or not, your bike-tire tubes will leak slightly, so tire pressure should be checked weekly. Too low a pressure, and you risk a flat from a pinch when you bang into something. I’ve had a few folks stop in, too, after literally blowing up their tire tubes with too much pressure from a gas station airing (high-pressure air, there). Tubes aren’t air tight.
There are those who are much more obsessive and check before every ride. Whatever floats your boat, I guess.
Bicycle tires hold higher pressures than car tires, so it makes sense, molecularly speaking, that bike tubes will leak more quickly. I’ve heard it said that car tires should be checked monthly. So, check your bike tires weekly.
I ride on 100-pound-pressure, narrow tires. I’ve aired them up on Saturday and notice already on Thursday that they aren’t carrying enough pressure.
Excuse me. I gotta check my tires.