[UA] Unspeakable Servants, Unnatural Phenomena

[Foster Ranney]

Some idle thought (players, don't read into this) has lead me to wonder something. I've got a question about unspeakable servants and the phenomena they can cause. Let's say that a group of people has upset a significant servant, and it wants to mess with them by dropping its one significant phenomenon per day. Can it just choose to have the group all suffer an hour of lost time - basically, to disappear and give it time to do whatever it wants in the meanwhile? That just seems ... unfair. Might it be appropriate to let characters resist the effect with a Soul roll, or is it fair to be unfair? I don't want it to look like a GM deus-ex-rulebook moment.

Short story: what are the sensible limits of a Servant's unnatural phenomena, especially as regards lost time?

Thanks for the help.