Why would it take hours to decode transmissions from Curiosity rover via MRO?

Question

This video clip by NASA says that data from Curiosity relayed by the Mars Reconnaissance Orbiter (MRO) would be stored for a few hours, then transmitted to Earth (apparently taking about 14 minutes), after which it would take hours for engineers to decode the data.

From what I've read, it seems that the MRO can be used as a backup communication device for Curiosity if needed.

In the case of Curiosity's landing, I figure the MRO would have store the data until it orbited around the red planet and had a direct line of sight with Earth before transmitting it (then again, I'm only speculating here), which I can understand.

But then why would it take NASA engineers hours to decode the signal relayed by MRO after it is received here on Earth?

(Bonus point: Does it normally take hours to decode MRO signals?)