You're certainly right that a daily candle opens at 00:00, but if it would end at 23:59:59, prices would have a gap of 1 second. I don't think that people want candles with gaps. Normally it's preferable when a candle ends exactly where the next candle starts.

And without using your time machine, I don't think you can enter a trade Friday and have it executed at the open of the Friday candle. Trades are executed at the open of the _following_ bar.

Trade platforms must take care of all those things to offer a realistic simulation - even if, no doubt, opening a trade backwards in time would give you great profit in a strategy.