Definitional issue. In everyday speech you could certainly say that it is. However as it's used here it's a constraint. For example "write the essay that's due

Definitional issue. In everyday speech you could certainly say that it is. However as it's used here it's a constraint. For example "write the essay that's due on wednesday" is a goal while "work on english homework for 30 minutes every afternoon" is a constraint. The difference is between a discreet event versus a general behavior.