I am of the practical belief that 10% is a good margin to allow.
I do follow the directions as laid out on the MR, and as this is a legal document I suggest you should to. No doubt some ambulance chaser somewhere would try and stick you for the replacement cost if anything was to go wrong.
I have been taught this rule by many experienced pilots and LAME's alike, but there is no reasoning for it - as per documents. I have only ever changed the oil and filter after a flight, as left to drain cold it takes for ever, and after runnning it in, the engine engine will not have scavenged the oil yet, and thus allowing a greater amount to be changed for clean - I think
As
pr the insurnance company. Ask for thier reccomendation and make sure you get it in writing if you are becoming a little sceptical. Most insurers are happy to work with you, and usually have some very knowledgeble and experienced staff on their books.
But I still agree with 5 hrs or as it is in most cases (10%).
