Here's a short guide to better understand how Max Raid Battle spawns and respawns work in Pokémon Sword and Shield.
Raids Spawn
It seems that the raids appear randomly in the hills of the Wild Area. As you have already guessed, the presence of a raid is indicated by a large beam of light in the sky, which descends into the den. You can then engage in a fight against the Pokémon in the lair.
Beyond the available raids, when you enter the Wild Area, you will encounter many inactive Pokémon dens. These seem empty to you. All you have to do is put a piece of a Wishing Piece on it and a raid will be triggered. You can make as many Dynamax raids spawn as you wish with this technique.
Wishing Pieces are available for purchase from NPCs near the Wild Area entrances, and will give you this item for 3000 Watts/unit.
Respawn of Max Raid Battle
Once you have done all the raids available in the Wild Area, other raids appear in places different from the previous ones and in unpredictable ways. Like some kind of reset. You'll never run out of raid combat !
In addition, if you want to make raids respawn at will, use the technique described above.
Reset and other processes
It seems that when you don't do any of your available raids or only some of them, they reset themselves. After a certain time (12 hours or less), the available raids disappear and change, to make way for other different Max Raid Battle.
There is an influence of time on this process. A change in the Switch's internal clock will probably modify the raids available in the Wild Area. It will also change the weather. Be careful, however, such manipulation involves risks for which you will be entirely responsible!
Another new big feature of Pokémon Sword and Shield is Dynamax. We will tell you all about this strange phenomenon that makes your Pokémon gigantic.
