I have chanced upon the following:
Overtime Allowance payble to Central Government Employees – Original OM
No. 15011/2/E.II (B)/ 76
Government of India
Ministry of Finance
Department of Expenditure
New Delhi, dated the 11th August, 1976
Office Memorandum
Subject: Overtime Allowance to Central Government employees.
2. Eligibility
All non-gazetted Central Government servants and also gazetted Government servants who fall in the excepted category mentioned at para 5(a) of these orders, paid from Civil Estimates (including those working in the Union Territories Administration) of the following categories, Vis. (i) office staff and (ii) those staffs whose prescribed hours and nature of work are comparable to those of “Office staff” shall in future, be governed by these orders.
Administrative Ministries will be competent to decide, in consultation with their Internal Financial Advisers, as to which staff falls in category (ii) above. The Comptroller & Auditor General of India will exercise that power in respect of the staff of the Indian Audit and Accounts Department.
https://www.gconnect.in/orders-in-brief/pay-allowances/allowance-orders-in-brief/overtime-allowance-central-government-employees-rates-ota.html