Have you tried fighting against the Wolf and Rat again? Should be in the same place and around the same time you fought them the first time.
I honestly can't seem to trigger these fights, these guys are nowhere to be found for me at all
You might be missing some conversations with Zorro or the tiger cop then. Besides that, opening the app in the Neighborhood or the Western District after midnight should allow you to fight them.
In what time can we fight them?
After midnight.