In the most basic of definitions, Days Working Capital tells you how many days you can operate before your working capital is gone. WC's equation is current assets(accounts receivable, inventory) - current liabilities(accounts payable). This tells you how well a company can pay off its short term debts.
The days working capital number tells you how well it can pay off its debt, but it can also tell you how efficient a company is. This is where the author made a mistake. A company with 10 days WC may be in better shape than a company with 90 days WC depending on how well they are operating. If a company holds almost no inventory by having suppliers who can deliver in a short time period, the company will save lots of costs by keeping inventory down, which will then lower their DWC.
Basically, if Apple stopped selling products and just sat there, they'd be bankrupt in 90 days. But this is unrealistic, and thus, the authors words were a bit over dramatic.
The days working capital number tells you how well it can pay off its debt, but it can also tell you how efficient a company is. This is where the author made a mistake. A company with 10 days WC may be in better shape than a company with 90 days WC depending on how well they are operating. If a company holds almost no inventory by having suppliers who can deliver in a short time period, the company will save lots of costs by keeping inventory down, which will then lower their DWC.
Basically, if Apple stopped selling products and just sat there, they'd be bankrupt in 90 days. But this is unrealistic, and thus, the authors words were a bit over dramatic.