There is no formal deadline. People will be submitting their forms far into the DV year. The only concern is that at some point it would be too late to get the form processed. However, the speed of processing varies by case, so I cannot put a finite date on the last time to submit. I would suggest treating May of the DV year (almost 1 full year after the results are announced), but I have seen cases submitted in June still get through.
So – it is perfectly fine to delay submission of the DS260, and in some cases it can be advantageous to do so (for instance where people cannot emigrate before completing college etc) .