Autotags are always converted to filter strings. Lets say you want to add firefox usage from 9am to 5pm.

Click on Applications timeline. Find Firefox in lower right corner, right click on it, choose Filter.

This will add some text to the bottom filter, and results will only show firefox.

Now in the filter append

[existing query] and start>9:00 and end<17:00

Or to show all activities after 9am you would just type start>9:00 in filter.

Then click on the arrow pointing down on the right side of filter textbox and choose Add to autotag.