I know it looks like referees like to swallow their whistles in the playoffs, but the numbers don't look much different through the end of the first round relative to the regular season:
|% of TOI||5v5||5v4||4v4|
Clearly the lack of 4-on-4 overtime reduces the amount of time spend at that strength. And the time spent at 5-on-4 relative to that spent at 5-on-5 is actually 2% higher. Not that this is particularly surprising - I looked at playoff penalty rates back to 1987 last season and didn't find general evidence of reduced penalty counts.