Hour starts from the beginning of the hour and ends at the end of the hour, and month start at the beginning of the month and ends at the end of the month:
| > Calendar.Hour()->beginning(); Calendar.Hour()->end(); | (1) Result: Hour(Thu 7 Apr 2011 16:00 CEST sharp) | (2) Result: Hour(Thu 7 Apr 2011 17:00 CEST sharp) | > Calendar.Month()->beginning(); Calendar.Month()->end(); | (3) Result: Month(Fri 1 Apr 2011 0:00 CEST sharp) | (4) Result: Month(Sun 1 May 2011 0:00 CEST sharp)
The beginning and end time has a length of 0 and is marked with the 'sharp' flag in the printout above. 0-length timespans might not do what you expect:
| > Calendar.Hour()->beginning()+4711; | (6) Result: Hour(Thu 7 Apr 2011 16:00 CEST sharp) | > Calendar.Hour()->beginning()+47110; | (7) Result: Hour(Thu 7 Apr 2011 16:00 CEST sharp)