As mentioned by WryLilt it is rolling 24 hours it will go up and down depending on the people who have visited it. In case of continuous traffic it will fluctuate faster. For your case a simple example will be as below.
1 day as per the view calculation is the last 24 hours. So if someone viewed your hub now that is at current time and no one else did after that then for twenty four hours it will reflect in the 1 day column. By default it will be already a part of 7 day column.
After 24 hours is over the 1 day column will reflect 0 as in the past twenty fours hours no one else has visited your hub. It is as simple as that. The 7 day, 14 day column will already have it added up. So you will see no change there until 7 multiplied by 24 hours has passed by.
I hope the answer makes sense.