Ouch - that's a rough one no matter how you slice it.
The problem is that either Alphartetta or Marietta is opposite of Ellenwood. From Alpharetta you'll wind up running 400 to either 285 east/south or I85/75 south through the city. From Marietta you'll likely shoot I75 to 285 west and come around the SW side or run I85/75 through the city. It also depends where in those areas you'll be - just getting to the main routes can be suicidal....
I can speak pretty good on all this - I'm an appraiser as well and planning travel times/routes is key to being productive for me. For me, this run is a 45 minute run off rush hour - in rush hour I'd say a good 90-120 minutes total barring rain and accidents. Of course ruch hour ranges a good three hours or so - say 6:30-9:30 and 4:30 to 7:30 or so.
Give me more specifics and I'm happy to offer possible alternatives - hang in there!
Hank Miller, SRA, ABR
Associate Broker & Certified Appraiser
Prudential Georgia Realty