Set Folder Date To Latest File Date?

Opus does preserve the timestamps if it can. Or at least it did when this thread was written:

Can DO Preserve Modify and Create Dates of Folders When Copy

Note that updating and existing folder may differ from creating a new one (not sure) and some filesystems or permissions prevent it from happening. And anything changing the folder will mess things up, as mentioned.

You may also find this thread useful as it has a PowerShell script which I think does what you want:

Change folder modified to date as same to the files inside