I would about Feb 1st, or earlier.

I start mine in early March -about 9,000 plants, 100+ varieties. They get transplanted into 2.5 inch pots in 4 weeks and are usually ready for sale two weeks after that at my nursery at the end of April. By Mother's day they are usually about a foot tall, healthy, stocky and ready to go in the ground. Although here in Northern VA we have had hard frosts as late as Memorial Day recently. If I started my plants in Feb they would be too big by May! I do a second crop in late March that are ready around Mother's day-about 6 inches tall or so. Once Tomatoes get growing, they grow fast! I sometimes pot up the little ones into an 8 inch pot and the roots fill the pot and the plant is 2 plus feet tall within 2 weeks. Be sure to provide lots of sun or artificial light (14 hours total) or they will get really leggy and weak.

Tomatoes sprout and grow quickly from seeds so early March sounds about right for Mother's Day. On the other hand, if you are growing say peppers, they may take about 3 weeks to sprout once seeds are planted.