When you're placing an order, you have to choose a Time-in-Force—day or Good ‘Til Canceled (GTC). Let's figure out how to place them and what the differences are.
The US stock market closes at 4:00 PM ET on trading days. If you choose a day order, all your pending working orders will be cancelled at 4:00 pm or 8:00 pm (if you choose to include the extended hours) if not yet be executed by then.
Suppose you want to invest in stock B, which is currently trading at a market price of $6.00. You place a limit order at $5.5. You choose a day order.
There are two possible scenarios:
A day order provides you with more flexibility to control your order placing. If you are worried the market will be too volatile on the next trading day, you can wait before deciding whether to adjust the price or not place the order.

A GTC order lasts until the order is completed or cancelled. Generally, all open GTC orders expire 60 calendar days after they are placed on Webull. You can place GTC orders during both regular trading hours and extended hours (from 4:00 am to 8:00 pm EST on business days), and you can modify or cancel your open GTC orders anytime.
Please note, in the event of any corporate action (stock split, exchange for shares, or distribution of shares), all open GTC orders will generally be cancelled.
Example
Suppose you want to invest in stock B, which is currently trading at a market price of $6.00. You place a limitorder at $5.5. You choose a GTC order.
There are two possible scenarios: