How long does Zantac take to work?

I checked the memories and didn't see an entry about this, so...
My 6 month old son was diagnosed with reflux and started on Zantac on Friday. It's Monday and we haven't seen much of an improvement. The ped said that we should see a difference by the end of the weekend and should see the full effect by the end of the week.

I was wondering what everyone's experience with Zantac has been. How long did it take before your baby got some relief? Did it not work in some cases? It seems like Josh's morning feed goes well, but he gets worse as the day goes on. I'm just hoping that we can fix this for him ASAP. Thanks in advance for your input.