The Montreal Canadiens made a run to the Stanley Cup Final last season, and with the schedule pushed back, that meant they were playing games well into the month of July.
The NHL schedule is usually wrapped up in the middle of June, with the NHL Draft then taking part in the second to last, or last weekend of the month and free agency opening on July 1.
Then, it is pretty much done for the summer months. Things were pushed back last summer, with free agency not opening until July 28, due to the global pandemic wreaking havoc on, well, literally everything in the world.