Complex sentence: The State of Illinois set a deadline of May 2011 to finish basic interior work and landscaping, but because of cold weather, the museum was given a 30-day extension on its original April 30 deadline.
Split into simpler sentences: The State of Illinois set a deadline of May 2011 to finish basic interior work and landscaping. Because of cold weather, the museum had been given a 30-day extension on an original April 30 deadline.