It is believed that you are located at a office of the bank e.g. branch/main branch/RO etc.
Usually the office are prescribed in appointment letter or by office order confirming change in office hours. The breaks are also described e.g lunch break, tea break. Bank office hours are usually say 10 am to 06 pm.
Including 1 hour breaks the office hours are 9 hours.
It is felt that the negotiations with the bank are based on Shops and Commercial Establishments Act
Kindly look into the Shops and Commercial Establishments Act in force in your State.
SBI staff association, has mentioned :
b) Normally, the total period of work including overtime shall not on any day, exceed, in the case of workmen other than members of the subordinate staff, 8 1/2 hours and in the case of members of the subordinate staff, 9 hours, excluding the period of recess. In case, however, of an emergency, of which a responsible officer of the Bank shall be the sole judge, or when the exigencies of Government work at the close of the financial year so require, a workman can be required to work in excess of the aforesaid hours. The provisions herein shall be subject to the provisions of any law relating to the ceiling on the hours of work or overtime applicable to the Bank. Branch Managers should ensure that employees are not permitted under any circumstances to work overtime in excess of the number of working hours prescribed in the Shops and Commercial Establishments Act in force in their States.
You can also check with :
Lalita Joshi, joint secretary, All India Bank Employees Association (AIBEA) and convener, women wing of AIBEA,
RBI bank staff regulation