Defense substitution strategy yesterday

It appeared there were multiple plays that the Bruins substituted a player on offense but we didn’t use the (what I believe to be legal) strategy of slowly substituting a defender, thereby leaving minimal time on the play clock. I’d think this strategy would have helped fluster an inexperienced Bruin quarterback if they only had a handful of seconds to make the appropriate reads. Did anyone else notice this too? Am I mistaken on this?