If you activate the onscreen help (click on the book icon on top right of the screen), you see the following information:
Note: Expiration of acknowledgements only works when using the Check_MK Micro Core.
→ not supported in checkmk raw edition, sorry.
Yes, this should probably be shown more prominently, not only in a “hidden” help text. Or even better, the GUI elements should not be shown at all in the raw edition or when not running cmc.
Regarding downtimes, please explain your problem in more detail. If it’s about regularly repeated (scheduled) downtimes, then again “(This only works when using CMC)” as is stated after the check box.