Query on DATETIME field

Hello, There is a common feature in the database I'm working on, that the transaction tables always have the DATETIME YEAR TO SECOND fields to store the creation and update time of the records. However, I encounter some reports which have to query on these DATETIME fields to yield the records within a specific period of dates. Since no index is built for these two fields, the time for getting the result is very long. Is there any enhancement I can make based on this design, so that I can get faster responds? Thank you! Samuel Tan