You can place the order once the status of Nifty is being shown as AH i.e. After Hours. Actually there will be some lag in your order execution so your order will be processed at around 9:57-10:00 am. For what its worth my 2 cents on placing an order between this timeframe is highly risky as during this time the price fluctuations are very high. Do wait atleast till 10:05 or so to place an order.
Just place your order as a normal order during After Hours and it'll be processed once the market is open.
Thanks