Extend the existing options (1 hour/day/week) with another one that allows to specify any number of selected units for all selected tasks to be moved (N hour/day/week). To be able to move tasks back, N should also be able to take negative values. In this way the existing options can be seen as shortcuts to the desired general one.
For example, if you want to move some tasks N days at a time, you can do that today only by moving the tasks N times by 1 day at a time. If you want to move the tasks repeatedly, you have to select all the relevant tasks individually each time. Tasks that have been moved too far by mistake cannot be moved back at the moment. These must then all be opened individually and changed individually.
This option would increase the flexibility enormously and would be a great help and reduction of work.