certainly didn't work when I sowed them in an unheated greenhouse. also if they start too soon on a window sill where will you put them say in March when it is still too cold to plant them out. I find a later sowing say March allows them to get up to size for going outside at the end of may.

Yes I've found later sowing better i sowed in mid July and it was still ok. I found that their was not enough light early on and plants would get leggy reaching for light and you got nowhere to put them anyway.