This is if you're trading at Zerodha:
For Equity/FO/CDS segment: AMO starts as soon as the regular markets close. AMO orders will be accepted from 4 PM onwards till 1 minute prior to market opening time, which is 9.14am for Equity and 8.59am for Currency. You won't be able to place any AMO orders from 09:15am - 4 pm.
For Commodity segment: After-market orders for commodity can be placed anytime during the day, orders will be sent to the exchange at 10:00 AM (MCX opening). So if you place an after market order at 9:59 it will get sent the same day and if you place it at 10:01 it’ll get sent the next working day.