What is deadline for the filing of lottery

My son has completed MS in Mechanical Engineering in May 2016 and also 12 month OPT (unpaid) which ended July 2017 . He is in US on OPT extension at present and is searching for a H1B sponsor. The company where he is working at present is e-verify but is not filing for his H1B . What is the latest that a company can file for the lottery that will be declared on 2 April 2018? The OPT extension will end 12 JULY 2019.

Please advise ASAP all options available at this critical moment

Thank you in advance