Well it can take a very long time, or a very short time. You could have bad regulators at those appliances, or a clogged line.
You should get an LP leak test, but only after all the appliances have been checked to make sure they work properly.
Leak test takes 15mins. Checking all appliances doesn't take too long. Maybe an hour or two. Fixing is the issue. There's no way to tell. Basically, if you want to use it, spend the money and time and get it fixed right.