I have drilled in May before. Apart from harvest maybe being a little later, the only other thing to look out for is BYDV. The crop is most susceptible at the 1-2 leaf stage, and normally in May the weather is warm enough for aphid migrations, so if the two coincide, it can be a major problem (esp. if you haven't applied insecticide or suitable seed treatment)We wont even consider drilling it until at least the second week in April or until the ground is warm enough,
you real need to put it in and its up in five days and never looks back, we drilled some beginning of March a few years back
almost a ton difference in yield to the April drilled and we have drilled as late as first week of May and got 3 tons acre.
Plenty of time yet as i said the ground needs to be warm.