Yes, that will work. Since you placed the 176:45 timer at the beginning, it will start the first On cycle at 2:56:45 am, run for 3:15, then repeat every 3 hours.
If you move the 176:45 timer to the 3rd position, it will start the cycle at midnight and repeat every 3 hours:
OSC 000:00/003:15/176:45 Then ON
Both ways work, just choose your preference of start times.