Active trinkets with unfavorable timers are more preferred than passive trinkets that procs right before downtime, even if cases where you may have to delay their usage.
Especially for Demonology as you generally always want a power boost timed with your HoG/CW as those are your most significant abilities. Specs like Affliction doesn't really suffer from 'timing.'
+ That particular case is solvable by Archimondes Darkness.
But overall there will be a wide selection of trinkets both passive and active instead of only/mostly passive ones as seen in MoP (the significant ones).