old-style FI system with a return = 2-3 seconds to refresh the lines
With newer returnless fuel systems, it could take a while, depending on how much fuel demand there is. Let's say 10 feet of 1/4" id tubing is about 95mL
One of Smokey Yunick's tricks for getting around regulations specifying a maximum size for the fuel tank in a NASCAR racing car was to use an 11 foot coils of 2 inch diameter tubing for the fuel line which added 5 gallons of gasoline to the car's fuel capacity. NASCAR officials listed 9 violation to be corrected before the car would be allowed to pass tech inspection. The NASCAR officials removed the tank for inspection. Smokey started the car with no gas tank and said "You'd better make it 10,", and drove it back to the shop behind the pits. He used basketballs in the fuel tank which could be inflated when the car's fuel capacity was inspected and deflated for racing.