Per the dash design, new weather data is loaded no more frequently than every 35 minutes, but can take longer between refreshes, as long as a couple of hours should the provider choose to throttle it. It appears this timing was originally agreed upon between Sony and their weather data provider. I don't see any external setting for it.
The way these agreements tend to work is that the parties agree and set up pricing for a budget of fetches for some period of time, either in aggregate or per device. The timer setting is then based on this - if the budget is exceeded then typically the provider returns an error. It sounds like the original agreement had individual devices fetch no more than twice an hour - it appears Sony added some slop to avoid problems, hence the 35 minutes.
My guess is that this agreement expired long ago, but that the service is still running just on momentum or goodwill on the part of the provider. In either case, it's probably best to leave it alone.