There are four contests during the regular season. The window during which the contest can be accessed on HackerRank is as follows.
Contest #1: completed
Contest #2: completed
Contest #3: completed
Contest #4: is available now; closes Sunday May 16 @ 11:59pm EDT
Based on the scores during the regular season, top students in all divisions will be invited to participate in an online Finals competition:
Invitations E-mailed: May 3, 2021 through May 16, 2021
Invitational Finals: Saturday, May 29, 2021 (Memorial Day weekend in the US)
There is a $25 per-student registration fee to participate in the Finals.
More details are available in the Finals 2021 page.