Quite literally, an opportunity cost is the cost of a missed opportunity, so yes, I would argue you are right.
In fact one would consider it an implicit cost. An implicit cost is what is left after the subtraction of accounting costs from economic costs. Economic cost calculating opportunity costs within it, will be greater than or equal to the accounting cost.
The accounting cost is simply whatever the firm has ended up paying. As the firm missed out on an opportunity by not paying earlier, its economic cost will be greater, but its accounting books will not show this difference.
- Carbaugh. Contemporary economics: an applications approach
- Mankiw. Principles of Economics