Since I haven’t seen a reply to this yet, I’ll jump in in lieu of one of the experts.
If you have the tariff’s setup correctly and “enabled”, you should only see it “work” if the calendar date falls within that time frame. It automatically changes to the correct tariff plan based on the calendar. I assume you have plans input and enabled to cover the entire calendar year.
Select the plans one at a time, hit “Load” and make sure it shows “Enabled”. As long as the the entire year is covered with your different plans, you should be good to go then, everything is automatic from that point.
On October 1st and June 1st, mine switch back and forth automatically. I have a feeling yours is probably working correctly, it’s just not super clear from looking at it.