Can anyone tell me the proper procedure to change the price range fields in Advanced Search and updating it to a time range field?

I already know how to change the labeling and many of the files where the changes occur, but I'm currently at a dead end.

I know that I would need to point to another field in the database, which I will create and populate with time data for each record (in a x:xx format---which I hope is OK with zen cart).
I made attempts at duplicating the code for price range and changing all the necessary data and labeling to time fields (with the Developer's Tools) but I'm unable to locate the area in the code which points to the database field that will be drawn upon in the search fields.

I need this updated area in the advanced search so that customers can find a song length within their requirements after entering a keyword search with a title.

Any and all help on the complete method of doing this is much appreciated.

thanks,
Jeff Michaels
Musical Creations Ltd.