I do agree it is about the growing on of seedlings when they have germinated and also about your location/climate that is the crucial thing and the space you have.
Having said that I started in January
sowed some Calenduals and some wallflowers already, outside in a cold frame in a sheltered spot.
Other seeds I start off on in an unheated propagator on my kitchen window sill.
You can sow snap dragons indoors from Jan which I did last year but it is all about the space you have to grow them on and what the weather will be like. If you aren't able to have a greenhouse then a cold frame is the next best thing
I always think it's best to look on the bright side so I'll be sowing a few seeds before the traditional advice just to see what happens