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: Pumpkin Saison; American Brown Ale(
Seconary: Don't use one, generally
Kegged: Pumpkin Porter
Planned: Either a Porter or a Scottish Strong Ale
"For a quart of ale is a dish for a king." - Shakespeare