There is something called "objCreationTimestamp" in OCUM db for all objects. This is the timestamp at which the object(objID) was created in dfm for a volume, qtree, aggr etc.
If you add a filer to a OCUM, which has 2 aggr, 10 volume, 20 qtree, then all of these will have the same "objCreationTimestamp", the time at which filer was added to OCUM.
Now if you create a new volume or qtree to this filer, the "objCreationTimestamp" will be within 15mins of obj created in filer.
As the discovery mon for qtrees, aggr, volumes runs once every 15mins by default.
So if that something OK ( 15mins, max difference between it got created in filer and discovered in OCUM) feel free to use objCreationTimestamp.
Regards
adai