Invite Method

This method does not need Nintendo Online subscription.
However, it will need a lot of patience. I prefer to only use this for a small amount of dates, but if you do not have a subscription, this is your only choice.
I recommend using touch screen for this.

1. Make sure your device Wi-Fi is on

2. Make sure your Y-comm is set to Local Wireless (not Internet)

(As you can see, NOT connected to Internet)
 

3. Enter a raid lobby (interact with your den), and Invite Others. Make sure the timer is there and counting down (as per the red box).

 

4. Now, Home on your Switch, and go to System Settings

5. Advance the day only by one, hit OK, then reenter the game

6. Now exit the raid lobby.


For however many days you have left, you gotta redo steps 1-6 for each day.
This method is pretty laborious, but if you're fast, you get down each day advancement to 5-6 seconds.