Hi pakujto ,
That column is calculated from an ATUM field called out of stock date. This field is set when there's a stock change that makes the stock reach 0.
So it won't begin counting until those products change their stock from positive to 0.
Hope this answers your question.
Best Regards,
José Andrés
P.S. We're working on changes to this logic, but they won't affect what I wrote above.