Updated (see below)
Reuters is reporting, as of 6:15pm Eastern Time, that the Libyan army has told inhabitants of the rebel-held Benghazi to get out of "rebel-held locations and weapons storage areas by 2200 GMT." Apparently the text was broadcast via Al-Libya television, telling inhabitants forces would be arriving "to support you and to cleanse your city from armed gangs."
10pm Greenwich Mean Time would be 6pm Eastern Time, so as of this post Benghazi inhabitants' time is up, and then some.* It is unclear from the Reuters report when, precisely, the message was broadcast, but it seems safe to assume it wasn't much earlier than an hour ago.
Saif Qaddafi earlier today told Euronews that "everything will be over in 48 hours." As the BBC reported at the time, however, correspondents think "the government probably does not have the forces yet to launch a frontal assault let alone to take the city in such a short time."
Thus far, no outlets are yet reporting an assault on Benghazi, though there could certainly be a lag. It's worth pointing out, too, that as of 6:15 Eastern Time Reuters was also reporting Muammar Qaddafi saying that there was unlikely to be a real fight to reclaim the city: "All the places where they (rebels) are fortified, are now being sterilized with the help of the people... who say where their locations are."
Update: As of 7:07 pm, Benghazi residents are telling Reuters reporters by phone that the city is quiet.
*Correction: We earlier incorrectly stated that 2200 GMT would be 7pm ET.