Not sure if I can do so , will there still be a lot of snow?
There shouldn’t be snow remaining in the valley during mid May, so you can bike around Hakuba no problem. One of the local tour companies in Hakuba, Evergreen Outdoor Center, begins offering mountain biking tours at the end of April. You may also ask them directly about biking conditions at that time, as they would know better than I. Or, you can take a look at this Hakuba cycling map or Hakuba Cycling website (both in Japanese only, unfortunately).
For hiking, the mountains will still be covered in snow, so I only recommend it if you have winter hiking experience. One of the most popular places to visit in Hakuba is Happo Pond, above the Happo One Ski Resort. This year, the Happo Alpine Lift from Happo Station will operate from June 2 to October 28, 2018. You can see an english map of the area here (ignore the 2014 dates). Again, Evergreen Outdoor Center may be able to give you more information about hiking and trekking around the area during mid to late May, so I recommend asking them for more information.
Another place I recommend to visit for hiking/trekking is the Nakasendo trail in the Kiso Valley. If you aren’t already planning to visit, take a look!
Let me know if you have any other questions.