SMS PDU-Mode
The Validity Period octet

Validity period specifies the time when SM expires. If SM is't delivered before that moment, it is discarded by SC. Validity-Period can be in three different format; Relative, Absolute and Enhanced.

Relative:

The TP-Validity-Period comprises 1 octet in integer representation, giving the length of the validity period, counted from when the SMS-SUBMIT is received by the SC. The representation of time is as follows:

TP-VP value	Validity period value
0 to 143	(TP-VP + 1) * 5 minutes (i.e. 5 minutes intervals up to 12 hours)
144 to 167	12 hours + ((TP-VP - 143) * 30 minutes)
168 to 196	(TP-VP - 166) * 1 day
197 to 255	(TP-VP - 192) * 1 week

Absolute

TP-VP field is 7 octets long, containing TP-SCTS formatted time when SM expires. See ETSI 03.40 for more information.

Enhanced

See ETSI 03.40