Pup Flyer
There is no general fixed rule on this. For most Lycoming/Teledyne Continental engines in general use you can apply through your maintenance engineer for an extension, on condition, of 20%. This 20% may also apply to the time limitations, so the 12 years may possibly be extendable to 14.4 years. You really need to ask your engineer who will advise you best for your particular engine..