You have to anchor them down in the hole, to give walleye a reasonable chance of grabbing them. Pockets can be fair secondary locations. Sandgrass adjacent to weedbeds can also produce. Regardless of the type of minnow you use, hook it lightly under the dorsal fin when fished off a straight hook and sinker on a set-line, and nose or tail when jigged. Set lines higher off bottom than you would when day fishing.
Walleye tend to feed upward, rather than down, at night.
Light plays a critical role in walleye fishing. Decreasing natural light at dusk triggers the bite. Usually, there's a flurry of activity in the half-hour or so before total darkness, then a complete lull for up to an hour, before the night bite commences. This lull is caused by a physical change within the walleye's eye. This takes a bit of time.