It is hard to tell until you actually check and no longer see "green" (then it is too late of course). Since leaf out could take a while and may not occur until Spring, I would make sure that they remain well mulched and that the soil is as evenly moist as you can (with no periods of dry followed by wet followed by dry and so forth). About 3-4" of mulch up to the drip line should suffice and should lengthen the days between waterings. Test the soil with a finger to make sure you are not overdoing it (insert a finger to a depth of 4" and water if it feels dry or almost dry). Pick up any plant debris under the trees & dispose in the trash or compost pile while you are watering. Before watering, amend the soil if your soil is alkaline so you do not have to water a second time after amending the soil.

How are you watering? I'd keep at it, because they can recover. Make sure the roots are being shaded--either by the plant itself or add a fluffy mulch (keep the mulch away from the base by a few inches). Don't use rubber or gravel mulch, use a shredded wood product or bark. Camellias have shallow, fibrous root systems and those roots need to be kept shaded from hot sun.

Keep in mind that Camellias can live hundreds of years. 30 is not old as Camellias go. One of the finest Camellias at the Huntington Library in San Marino was already well established plant when Huntington bought the property in--1906, and it's still there over 100 years later, and is still beautiful.

keep watering