Permanent tooth is loose - how long can I wait to go to the dentist to fix it?

Do not wait. Waiting only complicates treatment and increases risks to your medical health.
Sooner the better. A permanent tooth becomes loose when the surrounding bone starts to deteriorate, and is usually caused by a bacterial infection in the gums, or inside the pulp (nerve) of the tooth. The bodies self protection mechanism will try to rid itself of any infected irritant by continuing to loosen the tooth until it falls out. The sooner a dentist does a cleaning or root canal the better the prognosis.