Just had a quick look at the article and I think the bit that may have caused confusion is:
"Your engine will now need to be overhauled at TBO or 12 years, whichever comes sooner. The same extension period and ‘on condition’ rules apply to calendar time as they do the TBO hours period."
I think it means that the 'on extension/on condition' rules apply to both TBO hours and calendar time and affect the allowed useage of the aircraft as mentioned in the previous paragraph:
"If your aircraft is flown under what used to be termed ‘public transport’ (i.e. for operation by a flying club for training or private hire) the engine can be run for a further 20% of the time beyond TBO subject to certain conditions. For ‘private use’ you can run the engine
further ‘on condition’ subject to requirements detailed in the CAA’s CAP747 Generic Requirements Number 24."
Hope that makes sense!