When is the best time to apply grub control?
Can you help us with this confusion?

Late summer into Fall is the best time.
In spring,the larvae are already in cocoons.
This stage won't be affected by the insecticide.

We are having difficulty with grubs in the yard. Is there anything you suggest for this problem?

You can use a insecticidal granular called DeltaGard G Granulars , spread over
the area in the late summer or fall.

We have a lawn problem that shows up as small "hills" about the size of ant hills, but not the fine granular consistency normal for ant hills. The earth is almost in chunks. They seem to appear during the night, about 5 or more hills per night (small yard). Our neighbors don't seem to have the problem. The grass is quite thin in most places, especially where theses hills are.

Sounds like grubs. They are the larvae stages of certain moths and beetles.
You can spread DeltaGard G Granulars over the lawn and it watered in.