If anything it should be EASIER to light at night because the air is cooler and denser.
Try this: Shut the fridge off in the middle of the day, then turn it back on and see if it will relight itself. My guess is it won't be able to relight itself then either.
The only reason it lights off in the morning is because your husband lights it with a lighter. Things have also warmed up overnight; the fridge has some catch-up to do so it runs all day.
It is probably the location of the igniter. If it's not where the air-fuel mixture is good for ignition, it can spark until the cows come home. It's not going to light.
Right now the igniter is buried in a cloud of propane without enough air to light.
Moving the spark farther from the orifice should do the trick. There's less air, but the same amount of fuel, so logic would dictate that the fuel has to dissipate into a larger area to get a good air-fuel mixture.
