You Can Run, but You Can't Hide....

So recently, I received a phone call.  Let's say, hypothetically speaking - it was from a boy whom I may or may not be interested in.  Completely hypothetical.  And maybe not accurate.

Anyhow.

Let's say, hypothetically speaking, this individual asked for a quick response.  I am, hypot- oh, f' it -  definitely interested in speaking with this individual.  but maybe not at this moment.  Maybe I was not in the right mindset.  Maybe I need some time to 'organize my thoughts', if you will.   Maybe I just don't quite 'feel like it yet', if you will.

In the past, it was completely acceptable to take a day or so to call/email someone back.  It was understood that someone could be away from his/her phone/email for hours on end.  However, is that really believable (especially for someone in the 20-something range)?  At one point does someone realize that their contact has been received but is not being immediately responded to?  Your thoughts?