Uhh, my bad...
I reverted the installation procedure to the old one for version 0.15.1 which I just uploaded to extras-devel.
The "Clock & Alarms" entry is indeed a must-have.

Unfortunately, this means for some (those with some custom modifications to "/etc/hildon-desktop/status-menu.plugins") again that Advanced Clock Plugin won't work.
But for the big majority this restores the previous functionality.

Apparently, these are the trade-offs one has to accept.
At least until there is a better solution which applies to all of us.