Unfortunately, this isn't a current feature of TechTalk. However, it isn't hard to accomplish if this is a feature you'd like to see.
The current "work-around" is to go to "Advanced Search" (located below the search textbox in the upper right of every page). Use the dropdown menu for "Search Previous" to the desired about (1 day, 1 week, etc). However, because you can't search for nothing, enter a wildcard (a single *) in the Search Author textbox. Then do a search and it'll work.
If you'd like, I could add a drop down box to the index page (or, optionally, to each individual forum) where you would select the timespan and it will perform the search for you. (The index page would perform a search on the whole board, while a dropdown box on a forum homepage would, of course, be forum specific)
I hate to clutter up all of the pages with goodies and features no one would ever use, but if you would really like to see this, it's no problem to implement. However, for the amount you'd use it, is going to Advanced Search really too much trouble?