Final answer:
The statement that slack time is equal to LS-ES or LF-EF is true. Slack time refers to the delay a task can have without affecting the overall project timeline.
Step-by-step explanation:
The statement is true. Slack time, also known as float, is a concept in project management that refers to the amount of time a task in a project can be delayed without causing a delay to subsequent tasks or the project completion date. Slack time is indeed calculated by doing one of two things: subtracting the Early Start (ES) date of a task from the Late Start (LS) date, or subtracting the Early Finish (EF) date of a task from the Late Finish (LF) date. This results in either LS-ES or LF-EF, respectively. Therefore, if these calculations result in a positive number, there is slack time available for that specific task, and if it is zero or negative, the task is critical and must be completed on time.