Purchase a Digital Market Service from 1 February up to and including 28 February then the contract will start on 1 May with the reward due on 31 May 2018.
Early adopters of the DMS product are already enjoying their rewards. They received over £350 as their reward at the end of their first month of service.
So if you want to see your service start as soon as possible you should buy in February.
Time is running out.