Interesting puzzle Rod!
The cover and another that's on the Premier Postal Auctions site have both been sent from Rio de Janeiro so I guess the D.FEDERAL = Distrito Federal = the old Federal District which used to include Rio.
Could it be "4
A5 COLETA M" (4 to 5 Collection M), suggesting maybe a box was cleared at 5 o'clock?
Maybe with the M = da manhã = AM?
By the way, the cover on Premier seems to have a great story...
