Both breather and hiatus seem to be on the same timer according to raidloot. I haven't bought the disc to test it out yet on my monk, but:
It makes absolutely zero sense to use Hiatus with the 1000% weapon delay for 48 secs.
Breather is 90 sec reuse time and is 42 sec duration.
Hiatus is 6 min reuse time 48 sec duration.
Even if you pull in high dps groups even with chain pulling, you are going to have some point where you exit out of combat as the pulls get longer and longer. So you have a chance to hit Breather anyways.
Htw if you read this:
If this gets added to mq2melee, please make its own data entry instead of an updgrade to the Rest/Respite line or else if we have Rest=1, its going to choose this as the best disc over Breather.