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!