Official comment
Syncplicity provides link expiration (in days, not hours) that can be set on any file shared link, and can be required by policy setting so that all links have expiration within a max period chosen by the account admin.
In addition Syncplicity offers optional integration with IRM service that provides control over link forwarding, and many other uses of the shared files: restricting copying, printing, and screen capture of the file. It can also place a watermark on the shared files and restrict whether they can be accessed while offline. These are explained here:
https://syncplicity.zendesk.com/hc/en-us/articles/202673224
You'll need a specialized document management system to provide the kind of time-based controls you seek for file viewing.