Since pretty much everything can be instantly sped up by spending gems, where most players don't really purposefully use the option (Barracks anyone) the one thing where people might actually find a use for time reduction does not offer it: Generals travelling to and from adventures as well as troops travelling back from adventures without general.
In both cases, a moderate gem cost may significantly help players who have accidentally messed up somewhere to complete an activity on the same day which otherwise would force them to wait overnight.
I would think that for a cost of ~20 gems, the option may actually get used by players quite freqently, making it a valuable addition to the game as well as pouring money into Bluebyte's pockets.