If I understand it correctly, you want to block some categories for the phone from 6:00pm to 9:00pm, but want to drop the restrictions outside the time range.
The only way to do that right now is to assign the phone to the restricted profile at 6:00pm, and delete it from the restricted profile at 9:00pm. We are thinking about some design changes that will make this possible without human intervention, but you have to do this manually right now.
If it is possible to whitelist the sites you want accessible outside the 6:00pm-9:00pm block, then you can set up two calendars to achieve that:
1. In the restricted profile, add all domains (that are blocked by OpenDNS) you want access to outside the 6:00pm-9:00pm time range to the allowed URL list.
2. Add a calendar for the time range 6:00pm-9:00pm, with no domains listed.
3. Add a second calendar with two time ranges: 12:00am-6:00pm and 9:00pm-12:00am, list all domains you whitelisted in step 1.