I've read this API from here:
ZCS 6.0:Zimbra REST API Reference:Get Calendar - Zimbra :: Wiki

So if i pass in a query using this:

Its return me all the appointment inside the myholidays calendar in JSON format. Which is what I want.

But one thing I've consider is the size of the result. If after 1 year, I have around 100 appointment (which is less than actual), the result will be few KB. How about few years later? The size is growing.

Because the result will be used to convert to php native array using the JSON parser. I believe the PHP server do have memory limit per script execution.

I've checked out there is 1 parameter for the API called "start". Which allow you to specify +/- from the current time of the appointment should shows up.
But that only support atom, ics, rss, and ifb formatters.
But I want it in JSON format which is more easy for me to access.