I'm not planing to do any age checks and blow up the savedvars with all itemlinks to save the data, which will make the savedvars file >6mb
You'd need to save the itemlink, the time and date when the item got into the bag. And then check against this info each time the bag gets opened.
The savedvars file would get really big and the addon loading sloooow. No thanks.
My attempt is descibed above. Mark new items via FCOItemSaver with a chooseable marker item and hide the new marker of them if wished.
Nothing else.
Every other attempt can be done in another addon I guess.