How do you use the secret permits in guild retreat? I have 10 of them, but I don't see where to actually use them to add secret meditation slots in guild retreat.
In your guild base you can meditate to get some resources. However each guild base has limited number of available spaces to meditate. If all the spaces are full then you can use your secret permit to create a temporary extra space to meditate.
Honestly you probably will never need one. My guild base has 24 meditating spots and I have never seen them completely full even though my guild mates are pretty active.
I hope it answers your question.