The 9th U.S. Circuit Court of Appeals said backers of Proposition 8 - the state ban on gay marriages - have that long to ask the Supreme court to rehear the case.
The San Francisco-based court said it may continue to bar gay marriages even beyond that time if proponents of Prop 8 ask for a rehearing.
The Supreme Court's ruling earlier in the day cleared the way for same-sex marriages to resume, but sidestepped the larger question of whether banning gay marriage is unconstitutional.
The justices voted 5-4 to let stand a trial court's August 2010 ruling that overturned the state's voter-approved gay marriage ban, holding that the coalition of religious conservative groups that qualified Prop 8 for the ballot did not have authority to defend it after state officials refused to do so.
The practical effect of the Supreme Court ruling, however, is likely to be more legal wrangling before the state can begin issuing marriage licenses to same-sex couples for the first time since Proposition 8 passed in November 2008.
"While it is unfortunate that the court's ruling does not directly resolve questions about the scope of the trial court's order against Prop 8, we will continue to defend Prop 8 and seek its enforcement until such time as there is a binding statewide order that renders Prop 8 unenforceable," said Andy Pugno, a lawyer for the ban's supporters.
Gay marriage had been legal for 4 1/2 months in the state and an estimated 18,000 couples tied the knot before passage of Prop 8.
Gov. Jerry Brown said he has directed the California Department of Public Health to start issuing marriage licenses to gay couples as soon as the appeals court hold is lifted.
The battle over same-sex marriage in California started at San Francisco City Hall in 2004, when then-mayor Gavin Newsom ordered city clerks to issue marriage licenses to gay couples. On Wednesday, he brought the biggest cheers from the City Hall gathering when he said San Francisco is a city of "doers" that not only tolerates diversity, but celebrates it every day.
The measured enthusiasm contrasted with the exuberant cheers that greeted word earlier that the Supreme Court had struck down a federal law that prevents the U.S. government from granting marriage benefits to gay couples.
Associated Press writer Sudhin Thanawala contributed to this story.