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.