Robinhood managed to get 9-5PM EST trading, while Webull managed to get 5:00AM-8:00PM EST, which is much wider than Robinhood's. I wonder how they get permission and what is the limit, or it can be 24/7 except on Saturdays/Sundays?
A licensed registered broker in compliance with all SEC regulations does not need permission from the SEC to provide extended hours trading.
Brokers choose whether they want to offer it or not and many of those that do require that investors/traders apply for approval to do so.
Webull apparently just doesn't want to handle extended hours trading.
Extended-hours trading (or electronic trading hours, ETH) is stock trading that happens either before or after the trading day of a stock exchange, i.e., pre-market trading or after-hours trading.
After-hours trading is the name for buying and selling of securities when the major markets are closed. 1 Since 1985, the regular trading hours for major exchanges in the United States, such as the New York Stock Exchange and the Nasdaq Stock Market, have been from 9:30 a.m. to 4:00 p.m. Eastern Time (ET). Pre-market trading occurs from 4:00 a.m. to 9:30 a.m. ET, although the majority of the volume and liquidity come to the pre-market at 8:00AM ET. After-hours trading on a day with a normal session occurs from 4:00 p.m. to 8:00 p.m. ET. Market makers and specialists generally do not participate in after hours trading, which can limit liquidity.
Example chart of extended hours trading, via Google Finance Trading outside regular hours is not a new phenomenon but used to be limited to high-net-worth investors and institutional investors like mutual funds. The emergence of private trading systems, known as electronic communication networks (ECNs), has allowed individual investors to participate in after-hours trading.
Financial Industry Regulatory Authority (FINRA) members who voluntarily enter quotations during the after-hours session are required to comply with all applicable limit order protection and display rules (e.g., the Manning Rule and the SEC order handling rules).
Unlike stock options, transactions in stock do not have to be performed on exchanges. They can be traded between brokers as long as the price is the same as or inside the National Best Bid and National Best Offer (during regular trading trading hours).
However, brokers are required to report the transactions to the Trade Reporting Facility ("TRF") within 10 minutes of the transaction, and the trade reporting facility is only open from 8:00 am to 6:30 pm. However, the rules allow for transactions to be carried out after the TRF closes, as long as they are reported by 8:15 am the next day the TRF is open, allowing transaction to be carried out 24x7.
Some exchanges also offer extended trading hours, for example NYSE Arca starts trading at 4AM and continues on through the trading day into the after hours, closing at 8PM.
However, order protection rules only apply during regular trading hours (9:30 am to 4pm). Outside those hours, they don't apply which means that if you bid higher than the best price offered, you are not guaranteed to filled at that price offered. There is also less liquidity - which means that you might not get as good a price for your trade as if you would during the day (the difference between the bid and ask widens). The lack of liquidity is so detrimental that most institutions do not transact outside of regular trading hours.