WarcraftRealms.com

I wonder which purpose the status.txt has. Does the timestamp only relate to realm export? Because at least guild info is updated more often than the timestamp of the file changes (once per day). So is it a good idea to utilize the file to determine if guild information should be read from the local backup or from WarcraftRealms.com? Or may it be wiser to use a manual refresh delay like "if local file is older than x hours then pull fresh data"? That would also reduce server load (no status.txt is downloaded, websites would pull at different times). And how often may a website pull fresh data at most?

You should use the status.txt file always when determining whether or not to pull either guild data or realm data. The status.txt file is only a few bytes so it is much less server load than if any other data was pulled more than once per day.