Buddy, I haven't heard of any such thing & can't find any such extension ruling online. All they say is their office is closed to public (walk-ins) and sparsely staffed. I mailed mine in and got the stickers back in less than a week. I guess you could call your county clerk and ask.
I always mail mine in, and consider the $2.00 processing fee worth not having to spend the time, effort, and gas to drive downtown and stand in a line for 20-30mins.