Just adding to this my own point, I looked back at my (rough) transcript and the FBI guy twice quite clearly refuses to be drawn on whether or not there was a time in the ransom note. Then later, while responding to a different question, he blurts out that the deadline is 5pm today. That was my impression as I watched it. I wonder if that was 'accidentally on purpose'. Then when he's asked to clarify that it was 5pm, someone brings out a piece of paper and he walks away from the podium and checks it and then replies also giving the information he has twice refused to give before: the second deadline is Monday. JMO. Or JMI (just my impression!)
Part of me feels like a lot of this press conference was them cunningly sending messages to the abductor, or trying to mess with them in some way.