The OS automatically updates the folder time-stamp when an item within the folder is created or modified.
Thus in order for FlashFXP to preserve the folder time-stamp it would have to update the time-stamp after every other operation within the folder has been performed, and only then can it update the time-stamp. (it would have to start with the deepest folder first and work its way to the top-most folder.)
This would require allocating additional system resources and additional processing time to perform the operation, an operation which has very little real benefit.
For example simply changing the folder view in Windows Explorer can change the folder modified time or if the folder has images and the Thumbs.db file is updated.
So at this time FlashFXP does not attempt to keep the original date on folders.
Users familiar with Custom Command scripts can use an experimental command to set the folder date/time to match the date/time of the newest file within the folder.
/setfolderdate [-rc] <path>
This local command can be used to set the modified date of a folder to the newest item within the folder.
The r flag can be used to perform the operation on <path> and recursively to all sub-folders within <path>
The c flag will update the creation date to the oldest item within the folder.
This could be used manually via the RAW command input box or you could en-queue the operation and have it run as the last operation in the queue.
So if you had a queue entry for downloading files from a server in path \data\shared\ to your local machine path c:\data\shared\, you might right-click the local browser file list and select Enqueue > RAW command and then enter /setfolderdate -rc c:\data\shared\