Google released the first Developer Preview for Android 11 earlier than usual, but with that earlier release it means the company has additional time for tweaks inside of Android 11 before its big release in Q3 2020.
According to Google, we'll have a new pre-release version of Android 11 each and every month between now, and July. The initial preview release will be followed up by another couple of Developer Previews before the Beta releases in May and June, heading into the Final release in July -- but before that, Android 11 will be teased with the Pixel 5 smartphones at Google I/O 2020 in May.
The Developer Previews of Android 11 are not meant for regular phone users or even enthusiasts, and more so for developers so they can get their apps ready for Android 11 before it releases. Regular users will be able to use the Beta releases on their Pixel smartphones (except for the first-gen Pixel) when it drops in May 2020.