[T Bird]

No, it's not too early. You measure by placing the vial directly under the nozzle and having an assistant in the car press the accelerator pedal to the floor. Use an assistant-- you will get better results than if you try to activate the throttle linkage by hand from the engine compartment. Withdraw the vial and read the results. You can do this on the bench too, with the carb partially disassembled. Measure for each throat. The specified quantity reflects the amount of fuel discharged when the throttle moves from fully closed to fully open.