We can enable the reboot settings through Citrix policies in Active Directory Group Policy Objects (GPO) or in the Delivery Services Console (DSC). This results in some registry settings being added to the XenApp server under

HKLM\SOFTWARE\Policies\Citrix\IMA\Restart Options\Schedule:

RestartSchedule_Frequency -Frequency of scheduled reboots (in days)
RestartSchedule_Date -Reboot schedule start date, from the policy setting (in format of YYYY\DD\MM)
RestartSchedule_Minutes -Time of reboots. Its the decimal value, minutes past midnight, that the reboot is to occur.
RestartScheduleEnabled -Are scheduled reboots enabled or not through policy setting