i plant my seeds at the beginning of april in the greenhouse and the put them in the lottie at the end of may but keep them covered with fleece to keep any late frosts off them, they will need potting on again before they go outside,they are very greedy plants and i plant mine right on the edge of my manure heap so they get lots of feed, i then just let them meander down the edge of the allotment.
When planting the seeds in compost, because they are so wide they tent to rot it the compost is too wet so i plant them upright so any excess moisture drains away instead of sitting on top of the seed and find this works quite well.
Im still using the squash that i grew last year.