Go to > Control Panel > System Admin > User Listing > Edit a user > go to "Optional" Tab > on Time Curfew field, you can set the times when that user cannot login.
Time 
Accepted time frame format (* means all number):
...
| | | | | +--- Day of Week setting (3 letter abbreviation, such as MON, THU, FRI)| | | | | |
* * * * * *?
For Example :
User cannot login from 11.30pm - 11.59pm, the settings will be : * 30-59 23 * * *?
User cannot login from from 12am - 9am , the settings will be: * * 0-9 * * *?
note that you can add more than 1 settings, and it will be combined by the system. For Example :
User Cannot login from 11.30pm - 11.59pm and 12am - 9am. the settings will be :
* 30-59 23 * * *?
* * 0-9 * * *?
for each settings, you need to enter new line, so if you have 2 settings, you will have 2 lines of settings
Example 2:
User Cannot login from 11pm to 7.30am, the settings will be :
* 30-59 23 * * ?
* * 0-7 * * ?
* 0-30 7 * * ?
