Zantac isn't actually the best one to manage GERD symptoms long-term. Taking it as soon as pos gives it the best chance to work...if it doesn't help much take another as per the instructions. And remember...stay upright, eat SF, no spices, acid foods or cold drinks/foods!
Good luck.
PS. Ask your doc about Lansoprazole (Zoton)...it's the bees knees as far as I'm concerned. Kicked my GERDs butt! I only have to take it very occasionally now and I was getting severe heartburn everyday.