I believe I now have this working as intended.
This was a little strange to me to begin with because, even though I have worked with SDM for some time, I have never had to do anything with 'timespans'. When I read the document about creating queries based on time spam, I read that as a general English statement, not a specific SDM attribute.
Once that was cleared up (thank-you Jon and LIndsay!) and I created the timespan, I added it to my query but it still didn't work.
After some more research, I saw that I had to have TTV_enabled installed, which was not. I installed it but the query still didn't work.
Finally, I found another document that stated that TTV_enabled won't work if classic_sla is installed, which it was. I uninstalled it and now the query works.
Now, I just have to get the OK from my management to uninstall classic_sla in our production environment.
Thanks for the help!!!
Victor