nah, preflowers are simply a sign of maturity, plants will show preflowers most of the time at any light schedule, so long as they are old enough.. most of the time from seeds you'll see preflowers around 6 weeks or so in to the grow..
i usually like to wait till i see either preflowers or alternating nodes on my plants before i induce flowering as they are the two major signs that tell me that they are getting ready to reach sexual maturity and are ready to go to 12 / 12...