No person shall stop, stand or park a vehicle for any purpose or length of time other than for the expeditious unloading and delivery or pickup and loading of materials in any place marked as a truck loading zone during hours when the provisions applicable to such zones are in effect.  In no case shall the stop for loading and unloading of materials exceeds 30 minutes.
('65 Code, § 351.09)  Penalty, see § 76.99