There is high mortality of tilapia fry and fertilized eggs when water temps fall below 67F. This has been found in the laboratory where everything favors survival. As temperatures rise above 68F, mortality decreases and approaches maximum survival above 75F. There is really no way to get a head start. Until one's water is above 70F he isn't making baby TP. If stocked early, there is risk that some adults are lost before they are reproducing well. The adults that are at greatest risk are the females because they are smaller. Because they are not very fecund ... losing females which usually comprise no more than 33% of stocked weight would be very detrimental to forage production. Everyone would be wise to follow Zep's lead and wait until their water warms to a temperature they can breed successfully in.
The table below depicts the survival of eggs to hatching. The hatch rate at 68F is only 25%. The reference for this table is this
paper.