The firmware by default makes a call every 4 hours I believe. But the weather script caches the call result so across a day you will get the same watering percentage no matter how often you make the weather call. The main reason for this is that we want a consistent watering percentage across a day — if the number changes every time the call is made this can become confusing. Another reason for the caching is to reduce the number of weather queries — keep in mind that we pay for all the weather queries, users don’t pay any subscription fee etc. For us, weather quires are not free and can be quite expensive if we don’t control the number of calls.
If you’ve installed it on your own server, and do not have the caching, then the number will change more often.