Some speculation: It may depend on whether the jurors are following the instructions as a whole, or literally as written. Only if not following literally, would they have have reached the justifiable use of force instruction which is on page 12, after the murder and manslaughter charges.
The instructions state at the beginning that self-defense is a defense to both charges. So if the jury decided self-defense first, and found Zimmerman was justified in shooting Martin, they would never get to manslaughter to have a question about it.
If they hadn't yet determined self defense before getting to manslaughter, then they rejected Murder 2 on the state of mind element. If that's what happened, it seems unlikely they would decide the self-defense issue in an hour between dinner and now.
If there's a verdict now, and it's guilty of manslaughter, I think it's a rejection of Zimmerman's self-defense claim in its entirety.
Without self-defense, there's really no way to avoid a manslaughter conviction. All that it requires is that Martin be dead, and Zimmerman intended to commit the act (shooting him) that resulted in his death (which is not the same thing as intending to kill him.)
Zimmerman has never argued he didn't intend to shoot Martin. He's argued it was self-defense and he had no other means of protecting himself.
Put another way: The jury can reject murder 2 for one of two reasons: Either the state failed to prove one or more of the elements (such as ill will, hatred) or it found the shooting justified and not unlawful due to self-defense.)
If they reject murder 2 for the state of mind element, they are told to move on to manslaughter. If they reject murder 2 because they find self-defense, there is no need to move to manslaughter because self-defense is a defense to both.
So a guilty verdict on manslaughter means they didn't believe self-defense. It will be little comfort to Zimmerman that they also rejected the state's theory that he acted with ill will, hatred or spite for Murder 2.
But keep in mind this doesn't rule out a not guilty verdict. As one analyst just said, it's possible that four or five want to acquit and they only asked the manslaughter question to satisfy them. Maybe during or after dinner, they convinced the uncertain jurors. But again, had they agreed self-defense applied, what question about manslaughter would they have when the instruction states:
George Zimmerman cannot be guilty of manslaughter by committing a merely negligent act or if the killing was either justifiable or excusable homicide
And the justifiable use of force instruction clearly states:
It is a defense to the crime of Second Degree Murder, and the lesser included offense of Manslaughter, if the death of Trayvon Martin resulted from the justifiable use of deadly force
Surely they would have read the instructions all the way through, even if deciding the counts in order.
As to the theory this may go to 3:00 am because the judge has kept jurors that late before: Really silly, because while the judge might let the jurors go that late, she wouldn't have the lawyers and media hanging around the courthouse unless a court session was imminently expected. That the jury might have another question is no reason to keep the media around at 9:30 on a Saturday night.
My best guess: The jury will finish tonight. Tomorrow is Sunday, and they would most likely take the day off. If they are really close, why put it off until Monday when a few more hours would finish it tonight.
I'm not making any predictions on what their verdict might be if they return one tonight.