Hello @Maisa,
I apologise for the late reply.
I was hunting for a Houndour (levels 22-26) on route 7. My front pokémon was a fainted Baltoy at level 21, and a level 37 Natu was second in my party. I started around 9pm (in game time) and the repel trick was working normally until around 11pm. I was then unable to find any pokémon using the method until around 4am when I gave up searching.