I noticed in the New Horizon's release time schedule by Emily Lakdawalla/ Planetary Society that after July 20th, there won't be any data returns from New Horizons until September. Why is there a 2 month period of no data being returned?
From the same blog entry you linked to:
The transmission of the High Priority data set will be complete on July 20, and then image transmission will pause. For nearly two months, until September 14, New Horizons will switch to near-real-time downlinking of data from other, so-called "low-speed" instruments while it transmits just housekeeping information for all of the rest of the data. No new images will arrive on the ground during this time.
I read somewhere else that the "housekeeping information" includes e.g. the exact locations where photos were taken. This is seen as vital information (it helps put the data we already received in context), so it was given priority over the full image data.