Hi Chris,
This could be achieved using the time of day routing feature in CUCM.
Configure the same user extension with two different partitions and use one of them for timeframe 5.30 pm - 7.00 am with DND enabled ( this requires multiple time periods to be configured). Extension with other partition will be left as default so that it will ring in other time period which is 7.00 am - 5.30 pm.
You can refer the below guide for complete time of day routing configuration:
http://www.cisco.com/c/en/us/support/docs/voice-unified-communications/unified-communications-manager-callmanager/109588-tod-routing-example00.html
HTH,
Rajan
Please rate useful posts