"How long can they keep WDCZ silent?"
According to the rules published in fcc.gov, a station can remain silent for 10 days without even reporting anything to the FCC. Beyond that, they have to report it to the commission if they're going to be off for up to 30 days. They then have to apply for an STA (Special Temporary Authorization) if they plan to stay silent for more than 30 days. These STAs are usually a formality and last up to 180 days, and can be renewed if the situation warrants. for up to 12 months. If they're ready to resume broadcasting before their STA expires they can then power up once again like nothing had happened, unless a motion's made to revoke its license in the meantime for some other reason. Since that situation presumably won't apply here (AFAIK neither WNED nor Crawford has offended the Feds in any material way), if the proper paperwork is filed on time Crawford could have until the beginning of December 2013 to power things up and resume a normal schedule before their license is presumed abandoned and deleted from the records.
Usually a station that's changing hands and wants to make a total break with its past to re-brand itself and change its image will go dark for a shorter period of time (anywhere from 10 to 90 days) and then relaunch like it's a new station. In mid-June of 1984 Rochester's AM 1370, which had been WSAY and then WRTK, went dark for two weeks after being sold by the predecessor of today's Cumulus Media to the WXXI Public Broadcasting Council. It then powered up as WXXI-AM on July 2 of that year and has been in continuous operation ever since. Before then, at the beginning of the summer of 1930 Buffalo's WMAK (AM 900) was shut down by the Buffalo Broadcasting Company, which also controlled WGR and WKBW at the time, and sold to the Buffalo Evening News. 90 days later the News' new studio facilities in the Statler were ready and the transmitter was refurbished, so on September 8, 1930 WBEN made its debut as a new station and hasn't missed a day since.
Will Crawford's relaunch of AM 970 enjoy as much success as those two stations? Only time will tell.