Bonfire night (5th November) is next week, not this week.

People are letting off fireworks already so the sentence reminds these people that it is 'not' bonfire night currently and will not be bonfire night 'until' next week. They are making the point that setting off fireworks now is not appropriate and these people should wait until 'next week'.

Bonfire night is celebrated in a specific night, November 5th, but people have been celebrating it early even though the actual date is not until next week. It shouldn’t be celebrated until sometime next week.