can i buy an ETF and sell next day?

Yes, you can buy and sell ETFs on the same day, and this process is known as "day trading." However, it's important to understand the implications and considerations before doing so:

1. **Market Availability**: ETFs trade on stock exchanges just like individual stocks, so you can buy and sell them during trading hours. The major U.S. stock exchanges, including the NYSE and NASDAQ, have trading hours that typically run from 9:30 am to 4:00 pm Eastern Time.
2. **Order Types**: You can use various order types when buying or selling ETFs, including:
- **Market Orders**: These are executed at the next available net asset value (NAV), which is calculated after the market closes and typically posted by 6:00 pm ET.
- **Limit Orders**: These are orders to buy or sell at a specific price, which can help you avoid paying higher prices or losing money on a trade.
3. **Transaction Costs**: When buying or selling ETFs, you may incur brokerage commissions, which can vary depending on your broker. Frequent trading can lead to higher costs, so it's important to consider the potential impact on your investment returns.
4. **Tax Implications**: Depending on how long you hold an ETF, you may be subject to capital gains taxes. If you sell an ETF and it has appreciated in value, you may owe taxes on the gains. The rules around capital gains taxes can be complex, so it's a good idea to consult with a tax professional if you have questions.
5. **Leveraged ETFs**: If you're considering leveraged ETFs, such as the TQQQ you mentioned earlier, it's crucial to understand that they reset their leverage daily. This means that if the underlying index experiences significant gains or losses, the ETF's returns can diverge significantly from the index over longer periods.

In summary, you can buy and sell ETFs on the same day, but it's important to be aware of the market hours, order types, transaction costs, tax implications, and any specific characteristics of the ETF you're trading, such as leverage in the case of leveraged ETFs.