The best way to capture the information you want—the original creation/modification date of files imported to Laserfiche—is with Quick Fields. Quick Fields, through the use of Universal Capture, can import electronic file types from Windows. Additionally, it does have Windows creation and modification dates as tokens, which currently are not available through drag & drop or Import Agent.

In order to do this with Universal Capture, you will need to set up a new file type filter to scan in all files:

When using Universal Capture, you will see tokens for both Creation Date and Modification Date that can be used to fill in fields.