How long does it take on average to be promoted from private to Lance corporal in a infantry role

Its totally dependent on the individual, if youre keen, fit and show the potential you could become a lance corporal within a year or 2 however on average majority of people will achieve it by reaching 4 years service

To add to the above, it also depends on the forecast of events for your unit. For example, you could spend long periods overseas on operations or exercise. This will all add to the chances of promotion due to experience gained. It could mean a longer wait to get on a promotion course, all in good time!