I’ve a small thread on the terms and executing policy Seriously, Read the Execution Policy and the T&Cs
The execution policy explains the differences in orders and how orders will be executed Order Execution policy
In this case a trade outside of trading hours gets places as a basic trade, all basic trades get executed at 3pm.
Your right if you want to make a trade tomorrow on open then you can make an instant trade at that time (or a limit order under plus if you want a specific price and are busy).