Can an outdoor UPS be powered by street light circuit which is ON for only eight hours per day?

Yes. An extra-large battery bank will be required to power the load for a minimum of 24 hours, with expected battery lifetime of about 1.5 years (note: use of a 36- to 48-hour rated battery is strongly recommended if a battery lifetime of three or four years is desired). Also, this application needs a temperature-compensated, high-capacity battery charger which will ensure full charge of the battery after eight hours of overnight charging.