Wimpod respawn rate?

Wimpod respawns at a rate of every 24 hours. It's important to note that changing your clock will reset the respawn timer, so don't do that!

From here:

It respawns after 24 hours in all three spots. I messed up my route 8 spawn because my 3DS date was 2017 instead of 2016. Changing the clock resets the timer for another 24 hours.

This article also supports the 24 respawn timer:

once you fail on your first try you'll have to wait for its next spawn on the following day

If it's still not showing up, I'd recommend looking in the other two locations that Wimpod spawns. From this Serebii page, it appears that you can also find Wimpod in Poni Breaker Coast and Poni Wilds.