In short
A multi-site engineering program loses time at the hand-offs: a question asked at the end of one day and answered at the start of another, a slip in one site's tool that the other site hears about at the weekly review. Holding the program as one thing means one layer that reads every site's tools and holds every commitment to the one date, so a move in one time zone is re-planned for all of them within the hour.
Where the days go
Not in the work. In the gaps between sites: the status that has to be collected from each, the dependency that crosses a time zone, the re-plan that waits for a meeting all three can attend. On a program with a site in each of three regions, the week has three short overlaps and a lot of waiting.
One program, held once
Tymeline reads the tools at every site and holds the commitments across them against the one date. When a commitment moves in one region, the dependent work in the others is re-planned before their day starts, with the fix in front of its owner. The weekly all-sites meeting stops being where the program is discovered and becomes where decisions are made.