You can use lead and lag time indicators to specify:
The overlap between tasks (i.e., to designate that the next task(s) in a chain can start N days before its predecessor has finished).
The waiting period before the next task(s) in a chain can start.
You can specify lead/lag time only from the table portion of the Gantt chart. When you drag and drop a task on the timeline, lead/lag isn't automatically added.
Locate a task for which you need to indicate lag time (a waiting period).
Double-click the Predecessors column. If you don't see it, click the gear icon in the table's upper left-hand corner and check the box next to Predecessors.
Place your cursor at the end of the field and enter:
The - sign followed by a number to specify the lead time in days.
The + sign followed by a number to specify the lag time in days.
Press Enter on your keyboard or click anywhere outside the cell you're editing. You'll see the successor is rescheduled in accordance with lag/lead time.