Credit: Kevin Mazur/VF11/

The clock is ticking!

With only four months left till their August wedding, Jessica Biel, 30, and Justin Timberlake, 31, are still hunting for the perfect location.

Their musts? It needs to be in California and offer plenty of room! "It will be a big wedding," a source tells Us Weekly. "They have lots of people they want to invite."

Good thing the bride-to-be, 30, has enlisted help from future mother-in-law, Lynn Harless. "She's helping Jessica with every little thing," a source says.

As for the gown, the actress has already narrowed down her options. "Monique Lhuillier has sent over some sketches," says a Biel pal. "She's Jessica's first choice."

Though Timberlake, 31, popped the question over the holidays in Jackson, Wyoming, Biel didn't debut her 6-carat engagement ring in public until two weeks ago while exiting The Tavern in L.A. (Though she showed it off to Kristen Wiig and Amy Poehler at a Saturday Night Live cast party February 18, she was careful not to be photographed wearing her rock.)