If anyone ever attends a writers' conference, I would suggest approaching agents the first day there if you plan to pitch to them. Or, at least approach as many as you can, shake their hands. To me, this seemed counterintuitive. I thought it would be best to let everyone get settled in, relaxed, see my face around the conference -- then pitch to them days 2 and 3. I was also, admittedly, a little intimidated my first day. I wanted to feel everything out.
By days two and three, though, the agents were exhausted (having been hosting workshops AND getting pitched to by every attendee there).
I think agents are definitely exhausted by the end of a conference, but if a natural meeting doesn't occur on day one, don't sweat it! I imagine they're happy to meet writers even on the last day if it's done in a friendly, professional manner.
What about you, readers, what experiences have you had in approaching agents at conferences or similar events? I'm curious! Thanks for the tip, Kay!