This ticket is optional for PM-2330. 

SERVER-9507 lets us avoid a full index scan when $group and $first/$last are used together.  PM-2330 extends this optimization to timeseries collections, however it still unpacks the entire bucket containing the first/last data (with $internalUnpackBucket) and then uses a $sort and $last.

It would be more efficient to have a bucket access operator that directly returned the document for the min/max timestamp.