Given the following reasoning and answer, what was the question? The relevant information is: The idea of using 3-on-3 skaters for the entirety of a five-minute overtime period for a regular season game was adopted by the NHL on June 24, 2015, for use in the 2015 -- 16 NHL season.
The answer: June 24 , 2015 , for use in the 2015 -- 16 NHL season
The question Passage: In many leagues (including the NHL for regular-season games since the 2005 -- 06 season) and in international competitions, a failure to reach a decision in a single overtime may lead to a shootout. Some leagues may eschew overtime periods altogether and end games in shootout should teams be tied at the end of regulation. In the ECHL, regular season overtime periods are played four on four for one five-minute period. In the Southern Professional Hockey League, regular season overtime periods are played three on three for one five-minute period, with penalties resulting in the opponents skating one additional player on ice (up to two additional players) for the penalty for the first three minutes, and a penalty shot in the final two minutes. The AHL, since the 2014 -- 15 season, extended the overtime to seven minutes, with the last three minutes reduced further to three men aside and teams getting an additional skater for each opponent's penalty. The idea of using 3-on-3 skaters for the entirety of a five-minute overtime period for a regular season game was adopted by the NHL on June 24, 2015, for use in the 2015 -- 16 NHL season.

Question: Based on this passage, when did nhl start 3 on 3 overtime?