Aggregation on latest updated documents

I have a document which can be modified any number of times a day. I've ordered these document in time series creating index for each day. And each day would have multiple versions of the same document with different modified date.

Document sample:

id: 1234,
user: kc,
subscriptions: [
modified_date: 1466697434020
What I'm looking for is to get the latest documents in a particular time range for all users and to apply aggregation on top of it.

That would give a result like, in the last week/month how many people are subscribed for each of the papers.

Using top_hits I was able to get the latest document for different users in a time range, but I cannot apply further aggregations on this set of data.

Suggestions are welcomed, for changing the data model to achieve this.