RE: Alternative calendars and holidays, moon phases etc.

So let's say we have one virtual master clock that we all sync to by default
(though we can dereference to a US Navy clock or a sundial if we so wish).
How, at the most base level, do our applications interact with this - first
things that spring to mind are polls as one option, events another : do we
look at the church clock or listen for the bells? (must have been all that
talk of religion...) are there other alternatives?