Here are the steps:
- In a New Mail message in Yahoo click the Attach button.
- In the Select Files dialog, start typing a term in the search field and the Save button will appear in the dialog. For some reason, the Save button doesn’t appear when the dialog is opened.
- Click the Plus button next to Save.
- Select Last Modified in the first pop up and then Today in the second.
- Click Save.
- Name the Search. I call it 'Today.'
- Now, the Today Smart Search will appear under Saved Searches in the Select Files dialog -- no need to type the name of the file in the search field. Just click the saved search and all your recently modified files are together.
[crarko adds: I haven't tested this one.]

