In two years, criteria for enrolling into university are going to be quite different.
This is still idiomatic without "time".
"Rule": To add "time", place [apostrophe "s"] after the noun phrase. If the noun phrase is plural and already ends in "s", only place [apostrophe] after it. (Rules for singular words ending in "s" are too complicated to go into here.)
two years > two years' time
In two years' time, criteria for enrolling into university are going to be quite different.
The linked question asks how to insert "day or two" into the following sentence:
I'll be there in a _____ time.
Again, we can start without "time":
I'll be there in a day or two.
Following the above "rule" we get:
I'll be there in a day or two's time.