My take on it... From experience not FACT. Any ATC'er want to chime in?

I believe the release time is something you get every time you depart (to a large airport). The local controller gets it from the center to meet metering times. Usually a 5 minute window.

EDC Time (issued when their are delays) is a estimated time of when you might be released. They are updated every so often (30 minutes maybe). EDC's are not hard time and change. I've had controllers says they can call in 30 minutes to get an update. We have a system where we get updated EDC times over our ACARS. We usually get this before the controller says anything. Once we query them, they check on it and then we are released.

I don't think you asking him caused you a delay, you were going to get that delay next time he checked on your EDC.