Usually, depending on the complexity of the case, a quick verdict would not be a good sign (guilty verdict). If deliberations extend for days, hung jury is the likeliest outcome.
Oj, less than 4 hours. Not guilty. 7 week trial
I felt the same way about the OJ trial, when the jury came back after only 4 hours. I assumed he'd be found guilty (as he should have been) and we all were shocked at the verdict.