Alternatively, a data entry screen for Task name, Recurrence frequency, and duration that would create an .ics - formatted file that could then be imported into a calendar program. For example:
BEGIN:VCALENDAR
BEGIN:VEVENT
DTSTART:20131023T000000Z
DTEND:20131023T000700Z
RRULE:FREQ=MINUTELY;INTERVAL=15
SUMMARY:15 minutes (duration 7 minues)
END:VEVENT
END:VCALENDAR
that entry would then be duplicated every 15 minutes, e.g.:
BEGIN:VCALENDAR
BEGIN:VEVENT
DTSTART:20131023T001500Z
DTEND:20131023T002200Z
RRULE:FREQ=MINUTELY;INTERVAL=15
SUMMARY:15 minutes (duration 7 minues)
END:VEVENT
BEGIN:VEVENT
DTSTART:20131023T003000Z
DTEND:20131023T003700Z
RRULE:FREQ=MINUTELY;INTERVAL=15
SUMMARY:15 minutes (duration 7 minues)
END:VEVENT
BEGIN:VCALENDAR
BEGIN:VEVENT
DTSTART:20131023T004500Z
DTEND:20131023T005200Z
RRULE:FREQ=MINUTELY;INTERVAL=15
SUMMARY:15 minutes (duration 7 minues)
END:VEVENT
BEGIN:VEVENT
DTSTART:20131023T010000Z
DTEND:20131023T010700Z
RRULE:FREQ=MINUTELY;INTERVAL=15
SUMMARY:15 minutes (duration 7 minues)
END:VEVENT
[...]
END:VCALENDAR
etc.