As stated above, the average time will depend on which unit, as you will have to follow the guidlines in the unit training plan.
On average it is between 6 to 8 months, so for example at a smaller unit you may take 6 months with an average minimum experience requirement of around 200 hours and at larger units it will take longer due to a higher number of minimum hours probably around 300 - 400 hours.
These are just rough estimates, as it depends on previous experience, ability etc.
Hope that is of help.