Soviet agronomist Trofim Lysenko coined the term Jarovization in 1928. This translates to Venalization, vernum being the latin word for spring.
This study left my head spinning. What it boils down to is that plants know when to flower in spring because of sensors telling them it’s been cold for a prolonged period of time. When it stops being cold, the plants assume that it’s now spring. This makes the glorious spring blooms happen.
I’ve read on Growing Plants From Seed by “Doc” and Katy Abraham that you can chill your tomato seedlings right after the cotyledons, or seed leaves unfold. This is when they are about one inch tall. Do this for two to three weeks at fifty to fifty five Fahrenheit. This makes the plants stockier, flower earlier and produce up to two times the flowers in the first and second clusters.