On this page of our guide to V Rising you can find information regarding the length of the title. You will learn how much time you will have to spend on completing the main missions, and how much on doing every side mission and finding all secrets.
As V Rising does not have a linear storyline that you have to follow all the time, it's hard to say exactly how many hours are needed to complete the entire game. According to the producers, early access provides gameplay for 40/60 hours.
Players who participated in the closed beta in V Rising spent up to 80 hours fiddling with the endgame content. However, this is only the early version of the title, which will be constantly updated with new content.