I have a co-worker that routinely creates many small cases for similar tasks, and she'd like to be able to update the elapsed time on all of them at once.
For example, we're handle a lot of support calls, and she might have ten users than want her to add access to our systems. That tasks requires the same amount of time for each person, but right now, she has to open up all ten cases and update the elapsed times individually.
The elapsed time field on the case edit page shows the current amount of non-timesheet time logged to the case. We can't show the same field for multi-edit because the values for each case can be different and you don't want to replace the value with a new one, you want to add an amount to each. We have a case open to add an "additional elapsed time" field to the multi-case-edit page.
This could also be done via a plugin which displays the field if you're editing more than one case, then upon commit of the edit, it would add the amount to each of the cases. See the plugin architecture documentation on working with cases.