Hi Erin
We added workflow capability for tasks (and requirements) in v4.1, so please make sure you're running v4.1 and then you can:
- Go to Administration > Planning > Task Workflows
- Click on the 'Steps' link for the current Task Workflow
- Click on the status that you want the effort to be mandatory for.
- On the page that appears, set the 'Required' flag for the appropriate effort fields
- Click Update/Save
Regards
Sarah