I occasionally, when I think I am getting close to an elemental chest and it aligns with a bit of free time, will spend a gem or two on monster and raid chests to get them to pop at the same time. Never has this been an issue and I could accelerate the monster chest for say 1 gem and the raid chest for 2 gems at the same time.
This morning I intended to accelerate a raid chest and mistakenly hit the monster chest. Well, what I was greeted with was a 68 minute ‘cool down’ to accelerate the raid chest, exactly what was left on my monster chest timer before I accidentally accelerated it. I am certain this is new, and I am almost certain it was not disclosed as a change.
I don’t spend much to accelerate the chests, like I said, mostly to get it in a window of free time (with two kids that is tough) and this is now an inconvenience after playing over 2 years in this manner.
Will I live, yes, should this have been disclosed, yes.
PS - this is different than the cool down when you skip ahead too many in short order, this is allowing only one chest to be accelerated at a time.