Here's how they did it:
At 10 am San Diego Opera posted the following album on Facebook:
It included 6 photos. Each contained the name of the artist, their role in The Daughter of the Regiment and an additional word:
Bold letters advised the scavenger hunter to go to the 'aria serious blog' and look for the entry from Jan 15, 2013, which has been posted at 2:56 pm.
Which, when read forwards, said:
'Go to Facebook, solve The Daughter of the Regiment crossword.'
Back on Facebook, you would have found the crossword from last Wednesday:
The link lead to this crossword with the fifth and last clue:
Check our Facebook Page at 10 am tomorrow to participate in another scavenger hunt!