You can start Instant Streaks with your Best Friends, new friends, and friends on their birthday.
If you’re a Snapchat+ subscriber and you have Instant Streaks toggled on, you can start a Streak after sending a Snap back and forth. Instant Streaks are only applicable to a new Streak with any given friend—either a first time Streak or a reset Streak. If your existing Streak is eligible to be restored in the app, you'll be able to start an Instant Streak once it is no longer restorable.
To turn this feature on or off, go to your Snapchat+ membership page and toggle Instant Streaks on or off.