You can fill up 24/7, even if the store is closed.
I made the mistake once of needing gas on the NJ Turnpike, stopping at a rest area and having to wait for 45 (yes FORTY FIVE) minutes while the ONE attendant operating both sides of a single pump slowly worked his way through a massive line of agitated motorists. Never Again.
I also don’t drive that much these days so may be misremembering things. The only issue I had with payments was in a station in a small town in Italy which refused to accept most foreign cards (ant least based on other people around me also struggling) and was the automated no-human type of station so there wasn’t an easy solution.
10–15 years ago it was common in the US where you would pull up, hit "pay inside", pump all your gas, then go inside and pay at the register. Now because of theft, if you want to pay with cash, virtually all stations require you to go inside, pay for x gallons of gas, and they'll turn on the pump to give you that much. Which is annoying because unless you're really good at guessing, you can't just fill it up anymore.
Also no surprise they don't want you to pay cash, that means dealing with cash which is expensive.
Employees at the gas station could spend their time selling hot dogs instead :)
If you have two people one can wait, start it once the other pays, then you both go to the bathroom and pick up the change on the way out.