Use shortcuts for frequently used tags
Shortcuts can greatly speed up the time it takes you to tag your day. Click on a tag to select it, then type Ctrl-1 to assign it to 1. Now just select some time and type 1.
Use double click in Add tag window
Another time saver is double click on Add tag window. You don't need to select a tag, then click Ok. You can just double click on the colored square to quickly tag with selected tag.