running script at specific times without using cron [duplicate]

This question already has an answer here:

• Repeat a Unix command every x seconds forever 23 answers

I'm trying to run a shell script in (#!/bin/sh in HP-UX) on exact times(hh:mm:ss) hh:05:00 .. hh:10:00 .. hh:15:00 .. hh:20:00 .. hh:25:00 and so on. I understand this could be done using cron but I'm looking for another way to do this.

Adding: watch/repeat are not supported