You can very well say “I can’t afford that” or “I don’t have money enough to buy that” even if you technically have money in the bank enough to pay for something right now. Maybe you want some money as a buffer for unplanned expenses, or you’ve already agreed to but something that’s not yet paid.
Same goes for time: Yes you can choose what to do at any given moment, but the decision may already be made. You may have promised to do something - meet someone for lunch, go to work. Or you know that you need that time to sleep in order to feel well.
Surely it’s possible to change those decisions, the same way it’s possible to spend money in a restaurant instead of paying the rent. It’s not weird to speak of the decisions as final and the time already “spent”, though.