David Laurila at FanGraphs interviews starting pitchers about the differences from last season working with a pitch clock. Note that he speaks to rather good pitchers, and Shane Bieber‘s response was typical:

But for me, personally, I’m not finding much of a difference. I work pretty quick, especially without runners on. Last year, I think I was the second fastest without runners on base. 

FanGraphs.com

Good pitcher work fast.

I hope Laurila does the same question for relievers. Maybe he could identify the slowest working relievers from last season and see how they reacted to the clock.