IF I USE A GREEN MESQUITE LIMB IN A GAS BARBECUE

I like tilapia over hickory chips, but I've always done it by throwing soaked wood chips on hot charcoal briquettes. On a gas grill, since the wood isn't in direct contact with the heat source, how long does it take for the gas flame to get the chips smoking, prior to putting the meat on the gas grill? Do you experienced folks soak the wood chips, or not?