If you want to have a tremendous crop, "Super-crop" each plant before they get much taller. I usually do this when the seedlings reach no more than 3 or 4 inches tall.

Super-cropping means squishing the stems between your thumb and first finger (kind of roll it like you would a round toothpick), just enough to make the phloem (juice) come out. They'll wilt over for a couple of days, but if you don't squeeze too hard, they'll bounce back -- but -- with a stem two or three times as thick as ones you don't treat.

This causes the plant to be more robust, hold more weight and aids in maximum nutrient uptake.

When you are ready to transplant them, bury the "trunks" about 8 inches deep and even more roots will form along the main stem. You'll have gi-normous, robust, fruit-laden plants for your efforts.

PS I grow hydro tomatoes and do this to all my plants! :O)

l usually do it before planting the tomatoes

Here is a link that might be useful: When to Plant Tomatoes

Hi topher,
After potting up my tomato seedlings I let them readjust ( after a few days of top watering the soil settles a bit).
When seedling looks like has taken to it's new environment I sprinkle worm castings on the soil space ( carefully wet it so that it doesn't float over the side).
I don't cover the seedling's stem with the dry castings. But, when water levels the castings out some minimal particles' contact with the stem is OK ( scrape back any berm of castings from against the stem).
The plant will begin to grow showing robust development from castings' supposed growth hormones. Whenever I've run out of worm castings those normal, yet deprived, seedlings are comparative runts.
Store bought worm castings from a quality product should be potent if you don't wrangle worms. Some brands don't look or act like what my worm herd makes.
Sorry, I can't pass along a formal schedule of when precisely I do this, because have this chaotic way of keeping up with chores.