With <setdcalarmtime> it is possible to set a — absolute (independent from dive time) — time when the dive computer shall give an alarm.
(see also <setdcdata>)
<setdcalarmtime>
<datetime>T14:37:00</datetime>
<dcalarm>
<!-- duration 10 seconds -->
<period>10.0</period>
<alarmtype>1</alarmtype>
</dcalarm>
</setdcalarmtime>