I'd actually recommend since this is an A/T to leave the parking brake alone and just hold your foot on the regular brake. Then at the same time slightly rev the motor when in drive and also check it in reverse too with the help of an assistant of course. This can be more helpful than just looking for a brief moment of gear engagement to determine exactly how far the engine is flexing if at all. This is how we did it at the garage, keeping the RPM's in a reasonable range so as not to excessively abuse the transmission.
