Why a certain period of time is needed for promotion of qualified applicants? The main criteria for academic promotion to associate/full professor includes, research projects, publications, grants, administrative services, and such things. These are achievements that one can obtain regardless of timeframe. Logically, one with required achievements must be able to be promoted. However, most of universities need a certain period of time before promotion application (usually 5 years).

Why one must wait for promotion, when he is already qualified?

One who is associate professor for two years but qualified for full professorship must wait another 3 years to send application for promotion. Strangely, if that person apply for a full professor position in other university, he will be appointed as a full professor (if qualified) without waiting for another 3 years.

NOTE: the only criterion which seems to need time is teaching, but I think a strong/outstanding teaching records for different courses over 2 years is comparable with teaching the exact same courses over 5 years.
From my experience and what I have observed, the time frame is time for the academic to "earn their stripes", so to speak.

Some more factors that I have noticed that are considered, that do take some time to notice, namely:


The person's character - how well do they work with colleagues and/or students.
How the person performs under pressure and during 'down' times.
How much initiative the academic shows can only be observed over a period of time.


note: the above is not usually formally documented, but are important in any profession for someone going for promotion.

Also, as the university will be making a considerable investment in the academic, it would seem that they would like to see that the academic is willing to make a considerable investment (time, expertise etc) in return.