Hello Amberclaw,
That totally depends on which day you're arriving.
If the day is the early arrival day, no worries, no programming takes place on that day.
If it's the first official con day, yes, you will miss some stuff.
Last year you would've missed The opening cermonies and the sponsors preview of the art show, oh and the Barbeque and volunteers briefing.
Most panels start on the second day, but then again no promises, who knows what events will come up this year.