Good question, gpacker525.
When you connect an account, QBO will automatically download your transactions each night. Automatic updates run on a set schedule normally starting around 10 PM Pacific Time.
That being said, you can keep working in QBO while the accounts are updating as the process might take a few moments. You'll get a notification when the updates are complete.
You can learn more about it here: How to use automatic and manual online banking updates.
Just leave a reply if you have more questions. I'll be right here to answer them for you.