CAO 48 1 1.3 states that calculation of flight AND duty time shall take into account any flight and duty time performed in the course of private operations. We once had an operations manual section (approved !) that enabled us to count flight time but not duty time accrued in the course of private operations. I believe this was fairly common once, but is an operations manual matter, and not a CAO exemption. We were politely asked to change it some time ago.