Float is a discretionary measure of a schedule's flexibility or slack. While managers are most often concerned with overall network float variance along the critical path (Total Float), the float time for a single activity (Free Float) is also helpful in managing day to day operations. For example, if an activity has ten days of free float, management may decide to assign its intended resource to another task.
Free Float is the maximum number of hours or days an activity can be delayed without also delaying the early start dates of any immediate successor activities.
Total Float is the total maximum number of hours or days an activity can be delayed without also delaying the project finish date or another scheduling constraint. Total Float is calculated using the critical path method to determine the variance between early finish and late finish dates.