Get an addon that shows tick-marks on your channels. Try to wait until just after a tick to refresh, unless it's like a half second window of like all your procs being up at once, in which case getting all that SB:SS'd is more important.
Or really probably any single powerful proc is more important for full-duration dots than any single tick of MG/DS ... except possibly if it'd be your 2nd tick of DS in a row and you'd miss out on a shard that you really need.