As mentioned before, the way RSS feeds triggers work is by checking for any new feeds generated on the website within the last 6 hours and then triggering the workflow accordingly. So, if 1 feed is generated on the website within a 6-hour interval, your workflow will be triggered once. If 3 feeds are generated, it will trigger 3 times. If 6 feeds are generated, your workflow will be triggered 6 times, and so on.
In this case, changing the trigger interval time to 12 hours will have no impact on your use case. With a 12-hour interval, your RSS feeds trigger will search for new feeds generated on your website every 12 hours, retrieve all the feeds generated within that 12-hour window, and then trigger your workflow accordingly.
I can have the trigger interval time increased to 12 hours, but the use case you are describing is not possible because this is not how the RSS feed trigger is supposed to work; it will always capture all the feeds generated within this time period and trigger your workflow that many times, no matter if the trigger interval time is 6 or 12 hours.