The Commissioner has extended the time to enrol for the initial JobKeeper periods, from 30 April 2020 until 31 May 2020.
If you enrol by 31 May 2020, you will still be able to claim for the JobKeeper fortnights ending in April and May, provided you meet all the eligibility requirements for each for those fortnights. This includes having paid your employees by the appropriate date for each fortnight.
Source: Australian Taxation Office