I sow start of June into modules, this year I sowed on the 2nd and eventually planted them out july 16th, I think I repotted them once as the modules i use are small and they were a second crop after kohlrabi and early beetroot. But yeah you can sow them a bit earlier if you want. I put them under netting immediately or the pigeons eat them. I find them reliable and easier than most brassicas as you can just leave them out all winter.