Open the hive to do what?
If you are looking to pull frames and take the hive apart, then the temps should be at a minimum, when bees are flying strong.
There are many ways to check and inspect a hive during winter. You can check to see if a hive is alive by listening to the sides of the hive. This will also tell you where the cluster is located, how they are set for food stores, etc. You can also see how they sound compared to other colonies, this will give you an idea of cluster size and temperature stress. Listen to the hive, and then tap on the side, and see how the sound changes. If when you tap on the side the sound does not change, the odds are they are temperature stressed and generating all of the heat they can.
If the cluster is high in the hive and you want to see exactly where they are, if there is still food above them or around them that they can get at, I have opened hives during the winter on a "warmer" sunny day. Dont leave it open for an extended period of time. But, a short check does not seem to cause any problems.
But, I set my hives up for winter in 3 deeps or 2 deeps and a medium, with an empty box on top, then the inner cover and outer cover. I wrap the hive with black felt paper. I use the empty box for feeder jars in the late fall and again in early spring.
Yesterday, was a sunny day, high of about 29 / 30F. I still have feeders on the hives, so I checked all of the hives at my home yard. With a black felt wrap, 13 of 15 hives were up working the feeders and moving freely around the hive. I was able to put another 7 gallons of syrup on.
When I take the feeder jars out I place a sheet of newspaper on the top bars and a couple of pounds of granulated sugar on the paper. The paper does not cover the tops of all of the frames. The paper and sugar absorb moisture from the hive. Moist air can move up past the side of the paper and escape form the hive. But, if it condenses in the hive it cant fall back on to the cluster.
I find the extra box allows me to open the tops without disturbing the cluster, especially in late winter if they have gone vertical and are up in the upper box and need to be feed.