Yes there is a difference between say, five 5 second exposures and one single 25 second exposure. I leave the enlarger on and, by the beeper on my timer quickly move the card an inch or so after every three (in my case) beeps. In this way, each segment of the test strip has received a continuous exposure for the time in question.
You should also compare a dried test strip to a dried print. A wet print looks much different to dried one.