After 72 hours, you should see some slurry at the bottom of your starter. I'd say go ahead an brew with it.
Two Kids Brewery
Primary: nothing. :(
Seconary: Don't use one, generally
Kegged: A Midwife's Ale (Scottish Ale), Porter, Jenna Rose IPA
Planned: Belgian Brown Ale (loosely based on Corsendonk's Brown Ale)
"For a quart of ale is a dish for a king." - Shakespeare