You can come and visit the lake pretty much anytime of the year you want because most of the activities depend on the season. For example, if you are looking into climbing the waterfalls or skiing or any of the other winter activities, then you should come during winter, which is between June until August. There are also more winter activities such as ice skating and ice tubing that should be considered. The rest of the year you can do all of the other activities, including hiking, horseback riding, golfing, enjoying the hot pools and much more. The temperatures will be nice, but if it rains, then it will be cooler.
Just as a reminder, from October until April the area receives almost 12 hours of sunlight per day. However, during this time the country also utilizes daylight savings in order to offset the extra sun. The extra sun doesn't affect how any of the activities are run, except for that they might be open a little bit longer than normal.