It was very notable in game four between the Tampa Bay Lightning at Florida Panthers last night when a coach's challenge took upwards of 10 minutes to review. After the Lightning thought they scored to take a 1-0 lead, the Panthers challenged that it hit the netting above the glass prior to the goal. Eventually, it was determined it hit the netting, and the goal was taken back.
A video was shared on Twitter of the tablet that referees use to re-watch the play:
It appears that it's not only the officials taking their time watching the play, but sometimes it's the technology that takes its time to start working!