How to change an entire scene's estimated time

You can adjust overall estimated time of a scene by entering stripboard mode. 

Click the stripboard icon (Three horizontal lines) on the top right of the shoot day screen. Then click the estimated time for the scene and adjust it. Shot Lister will proportionally expand or shrink all the notes and scenes inside that scene to fit the new global time. 

This can also be helpful when first setting up a scene to quickly set estimated times to lots of shots.  For example, Iif you add a scene with 3 shots, all with 0 estimated time, then adjust the global time in stripboard mode to 1hr. Each shot will be adjusted to 20 minutes.