MachAF,
The EK cheerleaders on here will be quick to point out that the worthless "contract" you signed contains enough weasel language to allow EK to change the terms as you may understand them at their discretion if their "needs" dictate. The place is all about vagueness and deception.
Their "needs" strangely always seem to involve taking, reducing, or restricting something away you once enjoyed.
So no, these changes don't come at any set time, they come out as memos on an irregular basis. For example the changing of productivity (overtime) thresholds from 78 to 92 hours/month. That came out as a weasel-speak letter.
You join on one set of conditions, you are handed another. Please do get used to the idea if you plan on applying.