I have a basic question about testing and life trading.

I would like to trade only once per day, every day at 15:50-15:55, 5-10 minutes before the market close.

I want to check today's Close price and if the price meets my requirements, I want to enter the trade, for the same price (+- slippage). In real trading, I would check actual price from a broker, few minutes before the market closes and then send orders. When backtesting, I don't know what was the price 5 minutes before market close (I have only daily data), but for testing purposes, I can say that it was the close price.