I need to assign users at particular Calendar time

[Nani]

 I need to define a calendar so that issues created outside that define period will be assigned to a certain user (after hours support).

[Brant Schroeder]

Nani,

  We use automation for Jira to make assignments.  You can put in an if statement that uses JQL that looks at if the issue is created during certain hours. (created> startOfDay("+8h") AND created< startOfDay("+18h")) If it meets the criteria it will make the assignment.