How do I start with this? Any ideas?
Here’s something I modified from this site. It cycles through each item in a selection of multiple. This can get you started.
tell application "OmniFocus" tell front document tell content of document window 1 set SelectedTasks to value of every selected tree if ((count of SelectedTasks) < 1) then display alert "You must first select an item to complete." as warning return end if repeat with anItem in SelectedTasks set estimated minutes of anItem to 5 end repeat end tell end tell end tell