How late you fish for Walleye depends on the weather.
If it is overcast you can fish longer for them than when the sun is shining brightly.
I don't try to look for baitfish, that takes too long. If you have a good map, try and figure the migration routes used by the fish.
When I am targeting Walleye, I look for a likely route from deep water to where the fish will most likely be hunting for food. I set up on the route, and drill lots of holes all at once.
You don't want to be drilling holes once the bite has started. In the evening, the fish will start to move in from deep water to where they are going to feed for the evening. In the morning, the fish will start to slip back to deep water to spend the day the higher the sun gets.
Hope this helps,
Wiener