I has a serious discussion with our local CAA recently regarding compulsory maintenance items.
After two hours it was agreed (for private GA only):
1.ADs are compulsory;
2.Maintenance procedures/time limits in ICA (Instructions for Continued Airworthiness) are compulsory
3.Time limits as published in the TCS (limitations section of the POH) are compulsory.
Some clarification is coming from EASA later this year.
Note: time limits in the usual Maintenance Manual are not compulsory.