You can get a multiple test strip and the final print to match exactly.

If you are doing the timing by jerking the cardboard with the enlarger on, or using an analog timer, then results shouldn't be expected to match.

The turn-on and warm-up time for a PH-2xx enlarging bulb is on the order of 50 milliseconds, for the average 5-step strip with 5-10 second intervals this time can be ignored for most purposes. If you are using a cold-light then the only way to get really exact results is with a shutter, though you may find an integrator/compensating timer gives acceptable results.

An application note describing how to find the lamp turn on delay.