I believe that an earlier version of Dolphin enabled one to search for a file by date. This facility seems to have gone. If I wanted to to search for a Libre Office writer file modified last August,say, but had completely forgotten the file's name, I would enter *odt and a dialog box would offer me the opportunity to narrow the parameters to files modified between 1/8 and 31/8, and return a few files. Now the search will return hundreds of files. Admittedly it is quick to sort by date, but the list takes much longer to create.
Use kfind. The KDE team removed the integration with kfind sometime last year I beleave.
I found a solution in kubuntuforums on how to create a service menu. If you do it this way you will find the "Search with kFind" in the action menu, when you right click on a folder.
Save the above text as ~/.kde/share/kde4/services/ServiceMenus/kfindhere.desktop (for specific users) or /usr/share/kde4/services/ServiceMenus/kfindhere.desktop (for all users, I have not tried this)
If you are not opposed to using the command line, you could use something like
to find all odt fies modified that were modified less then 133 days ago, but more than 102 days, which for toady is just files modified in August.