for standard rest pause, 30 seconds. though you can wait 5 seconds, 10 seconds, or anything in between. consistency is key though, as it better tells you if you're making progress.
for example, 5-10 second rest, you'll get maybe 1-2 extra reps. on a 30 second rest, you may push 5 extra reps. if you're not consistent with your timing, its difficult to measure progress.