Stock Time is how long we expect the product to be in stock (before it is sold out). Expected demand is taken into account here.
Generally, these metrics are well known and have multiple ways of being calculated; hence, if you notice some discrepancies, it is because you could be using another formula. Also, please keep in mind that these metrics are dynamic and can change based on our calculations of demand, changes in average stock, etc.
The 'Stock time' is calculated as:
Stock time = number of days such that the total amount of sales in those coming days is equal to the current stock on hand.
Example: if the current stock is 6 and the forecasted sales are going to be 4, 1, 2, 1, 1 in the coming days, then the stock time is 3.
After 2 days, you have sold 4+1=5, which is less than the current stock, on the 3rd day, your stock will be -1.