Every turn:
If the minutes part of time of day is 0:
say "The cathedral bells chime [hours part of time of day] o'clock."
EDIT: To avoid odd announcements like ‘The cathedral bells chime 13 o’clock’ if your game stretches into the afternoon and evening, one of these these modifications might be advisable:
Every turn:
If the minutes part of time of day is 0:
say "The cathedral bells chime [if hours part of time of day is greater than 12][hours part of time of day minus 12][otherwise][hours part of time of day][end if] o'clock."
or
Every turn:
If the minutes part of time of day is 0:
say "The cathedral bells chime [hours part of time of day] times, signalling [if hours part of time of day is greater than 12][hours part of time of day minus 12][otherwise][hours part of time of day][end if] o'clock."