There are some indications that "stressing" the plants somewhat will give earlier tomatoes. In practice that means leaving them in a small pot a bit too long. They will switch to flower production because of the stress, instead of staying in the growth phase.
In theory.
I have some anecdotal experience with it and this was confirmed by the experiences of someone else. But I haven't done side by side comparisons yet, so it could all be nonsense/biased observations.
I think I started mine too early again, although I started later than last year. There isn't a problem right now, but once I need to start transplanting them I will run out of space soon.
Here is one tray.
These ones are mostly bush types suitable to colder conditions and are meant to go out a bit earlier than others. Maybe in the second half of May.
I was a bit fooled by the weather. In march (most tomato seed sown in the beginning of March) spring had seemingly started after an extremely mild winter. But now it is pretty cold again. It even snowed this morning.
On sunny days I can put my seedlings in my unheated greenhouse after 10 AM. At 9 AM there are often still iceflowers on the windows of the greenhouse. Around 3PM they have to come inside again, because the sun can't reach the greenhouse any more. The sun is pretty low in the sky still at this time of the year.
Logistics though. I am aiming for 100 to 150 plants this year. And I obviously do not have any space on the window sill for that. So I need sunny days and agreeable temperatures so the plants can go to the greenhouse during the day. I know that in late april and beginning of may I will have a logistical nightmare unless spring is exceptionally warm.
Maybe I will learn my lesson this year and plant most of my tomatoes in april next year.