Timer form ask you to input hour, minute and second. For absolute timers it is time in the day when alarm should happen. For relative timer this values specify interval since current time. If timer is periodic, then relative time will produce alarm with the period equal to the specified interval. And periodic absolute timer will produce alarm each day at specified time (so period is 24 hours).
Timer midlet provides several way of alarm notification: sound (it is possible to configure frequency, volume and note of the signal), vibration, backlight and sending SMS. Also it is possible to specify duration of the alarm - period within which sound, vibration and other effects are produced. In case of alarm midlet shows model alarm alert which is visible until user execute "Dismiss" command. The command also stops sound, vibration and backlight. To me able to send SMS, it is necessary to specify destination phone number in settings. Unfortunately at most of the phones this mechanism will not work since phone will ask user permission for midlet to send SMS each time when it tries to send SMS.