Depends on how fast you get on course realistically. However as an AERE, and most other eng trades you will be captain in 2 years no matter what, and if it takes longer than that you will be backpaid for all the extra time as a captain pay.
Ocdt is 3 months in basic,
2Lt is 8-14 months (14 months for AERE, not sure about the others)
Lt comes after 1 year, or after you are operationally qualified.
Captain is 1 year after that.