Under JAA procedures, AMCs were, indeed, purely guidance and many were routinely ignored; however, under EU law, things are a little different. Where a single AMC is published in relation to a requirement it represents the only acceptable means of compliance. Any person or organisation may propose an alternative means of compliance and, if accepted by the competent authority, either means may then be used to comply with the relevant requirement.
However, whilst the AMC in this case is, to all intents and purposes, mandatory, the amount of training is not. The ATO 'can' take into consideration the training times quoted in the AMC, it can equally well decide not to and it is probably worth shopping around to find the easiest and cheapest route to renewal.