Schedule Development
Building the network
Schedule development converts the plan into a logic-driven, calculated model. Essential concepts: activity sequencing with finish-to-start, start-to-start, finish-to-finish, and start-to-finish relationships plus lags; duration estimating bases; forward and backward pass; early and late dates; total float and free float; critical path as the longest path through the logic; multiple critical paths; constraints; open-ended activities; and schedule quality checks such as a recognized 14-point assessment. Resource leveling changes dates, while smoothing consumes float without extending the finish. Negative float signals a deadline or constraint conflict, not a calculation error.
Traps: selecting the path with the longest activities instead of the longest logic path; treating lags as real work; confusing total float (delay tolerated before project finish moves) with free float (delay tolerated before the next successor moves); using constraints to force dates and thereby mask missing logic; and leaving open ends that corrupt float results.
Worked example: activities A(4d) to B(6d) to D(5d), and A to C(2d) to D. Path A-B-D is 15 days; A-C-D is 11 days. Activity C has total float of 4 days and free float of 4 days, because D cannot start until B finishes anyway.
Rule of thumb: trace the critical path through logic, confirm no open ends, and verify total float = late finish minus early finish for every activity before reviewing the finish date.