Probably "whenever you want" as long as you have the light and your location does not get too cold.
Also if you are growing them a long time inside, you will want to plant the seedlings into pots so they have room to grow whilst they're inside.
I'm lucky here in Texas in that our last frosts are in March so I can get away with sowing them outside, but sometimes I'll start them a few weeks earlier inside and then plant them directly outside. Allow two weeks for germinating, and with another 2-3 weeks they'll be ready for taking out of seed trays and putting into pots. Keep them in the pots until May.
I soak the seeds in a salt petre (potassium nitrate) solution before sowing - this is meant to help with the harder to germinate varieties, but I have not done any side-by-side tests.