After 72 hours, you should see some slurry at the bottom of your starter. I'd say go ahead an brew with it.
Brody's Brew House
Primary: Scottish Strong Ale
Seconary: Don't use one, generally
Kegged: Sweet Potato Saison
In the fridge: Czechvar, New Belgium sampler
Planned: Either a Porter or an AIPA. Possibly a RIS.
"For a quart of ale is a dish for a king." - Shakespeare