At this point, it's dependent on the team you interviewed with how long it takes to hear back. Some are very good about passing on decisions to HR immediately, but others might take longer as they wait for more candidates, or it just gets pushed back for other projects.
None of the teams I interviewed with had second interviews, but for the 3 that I did interview with the team for, it took 2 months, 1 week, and 2 days to hear back on their decisions
That's not much help, but I believe the summer positions start in June? My last minute role was interviewed/offered a month before the start, so I would expect most acceptances to go out by the end of the month