Scheduling is a lot easier if you are looking a few days out, and your schedule is very flexible.  But for a lot of us, it tends to be more of a "oh, my calendar just freed up this afternoon" or "maybe I could sneak away tomorrow morning for a little bit."  I used to try to exploit those opportunities.  But it ends up being a whole bunch of voicemails, a whole bunch of emails sent, and then there's still less than a 50/50 chance that something actually works out.  It is such a let-down that I don't even try that often any more, it just isn't worth the frustration.  I am not saying that anyone should be camped out by their phone 24/7 waiting for my call.  I'm just saying that I literally meet up less than 1/8 as often now as I did ten years ago because there's almost no chance that you can set something up short-notice, and often, you've invested an hour plus into calls and emails before you find that out.