Hokkaido Driving in Feb

Hi, i am planning to drive in Hokkaido in late Feb, from Hakodate to Otaru or vice versa, and i have a few questions to ask.
1. What is the average speed on the highways during Feb?
2. Northern-road.jp/navi estimates 3hrs 14min from Hakodate to Toya Onsen, 172km w/o using expressways, but the time estimated is not during winter. How long more should i add to have a good estimation for travelling time in winter?

thank you for your time :)

What is the average speed on the highways during Feb?

It depends on weather conditions, especially on whether there is snow on the road or not.

If there is no snow on the road, people typically drive about 20 km/h above the speed limit. The speed limit is usually 40-60 km/h on regular roads and 70-100 km/h on expressways.

When there is snow on the road, people drive with reduced speeds.

Northern-road.jp/navi estimates 3hrs 14min from Hakodate to Toya Onsen, 172km w/o using expressways, but the time estimated is not during winter. How long more should i add to have a good estimation for travelling time in winter?

Again, if there is no snow on the road, you should be able to travel with a 50 km/h average, i.e. do the trip within 3 hours. The specific area (Hakodate-Toya) does not usually have snow covered roads.