If I ever decide to add a fuel pressure gauge, I was wondering if I should wait a certain amount of time after turning the car off before unhooking fuel lines and all that.

 

Yes, it does keep the lines somewhat pressurised. Start the car, then remove the fuel pump relay. When it stalls, keep cranking the car over for a good few seconds. After that, there should be little to no fuel left in the lines. It is still good practise to keep a rag handy, as some will always remain to drip all over your hand/tools/paint/floor.

 

In theory, bleeding the pressure from the fuel lines is the Right Thing To Do. With proper goggles my standard practice is to just crack the lines open and do the work. Don't smoke or start the engine until it's dry/evaporated.