The way the lag field under the links tab in the task properties window receives focus is super frustrating because it requires multiple clicks in order to start editing the number of days. First, you click on the field. Then, you have to start type for it to receive focus. Then, you have to preposition the cursor with the mouse onto the numeric value. Now (finally!!) you can actually edit the value. Makes me want to tear my hair out.
This happens consistently whether or not "begin typing to edit cell" is selected in the options menu.
You should be able to click on the field and have the lag duration immediately highlighted and ready to edit, so all you have to do is type in the new duration (the scroll thing to change the duration is virtually useless unless you are changing the value up or down by a single unit).