You're right about
the timing of Zantac is very important. It's common to take 300mg at bedtime, but it should be at the latest possible time, because as you said, it's not time released.
The other option (if you're having trouble during the day) is to try taking another 300mg in the morning. Here's a good discussion about
the uses of drugs that are effective in treating GERD and esophageal erosion.www.medicinenet.com/gastroesophageal_reflux_disease_gerd/page6.htm
Good luck working it out! You might try discussing it with your pharmacist. They're often very helpful and have lots of information at their fingertips.