Payment of allowance to the employees who work in night shift is company-specific employee welfare. As far as labour laws are concerned, no law says that night-duty personnel should be paid some allowance. Therefore, you may approach your company officials or the HR department and ask for the night-duty allowance.
By the way, if the afternoon shift ends at 2230 hours, then the employees are not working even half of the night. In that case, what makes them think that they are eligible for the night-shift allowance?