There isnt a standard IEC timer with retentivity.
But in the standard library under TI-S7 converting blocks you can find FC80 TONR which is a timer with retentivity.
Notice that it uses DINT and not TIME for the setpoint. It is basically the same (the time measured in milliseconds).
Also notice that you have to copy #OB1_PREV_CYCLE in OB1 to a variable that is loaded into FC80 at DELTA_T.