When your principal tells you and you receive the letter or through pac gov???

You can more or less Guess you will be promoted if you have consistent grades or upward trend grades. Usually, last year grade before promotion is the highest of last 3 PB grades. Most of my colleagues, average degree holder performance is 2 years to GEO3, 3 -4 years to GEO4.

For promotion to GEO 5, it depends. Some people take 2 years, some colleagues even 5 years still at GE04.

Above are all first career Teachers for my school colleagues. Mid career should be faster but the expectations will also be higher.