Hey there

The purpose of the workout is to make your pinky stronger and faster, and also to work on timing. If I understood correctly, you have a problem when hammering-on with pinky, it is not done in time?
If that is the case, I can recommend you to practice in very slow rhythm, note by note. Don't worry about the speed now, first need to master it in slow rhythm and then gradually increase.
I use metronome occasionally, before used it a lot and now just when have to practice something difficult. Now when I work on timing I rather do it with some drum loops

I would be able to help you more if you upload your performance, to actually hear where's the problem.