I'm not sure I understand the details.
Do you mean that you have two separate Data Adapters
and that you need to measure time consumption for all the items supplied by the first Data Adapter and only for them?

In this case, admittedly, if you define a single Adapter Set which includes both Data Adapters, you will incur in a Metadata Adapter interface limitation.
In fact, the Metadata Adapter is notified about the beginnig and the ending of the subscription of each item and the involved user name is also supplied;
but only the item names are supplied, not the related Data Adapter IDs.

Hence, if you can distinguish the two sets of items based on the item names only,
then you can treat them in different ways in a common Metadata Adapter;
otherwise, things would become complicated with the single Metadata Adapter approach too.