FWIW, there's a lot of pretty cool and effective timer apps for free to use on a smartphone. Mine even lets me set the music to the round!

Workout:
135# Clean & Jerk 30 reps
5:15

2min rest then 6mins to work up to a 1 rep max Clean & Jerk.
205#. I failed at 215#. Pretty happy considering that's a C&J PR for me and doing so while tired!