Hello @Sampreeth Inkulu ,
Welcome to the Microsoft Q&A platform. Happy to answer your question.
Yes, this is the expected behavior. If you update the auto shutdown schedule for your VM within 30 minutes of the previously scheduled shutdown time, the new shutdown time takes effect the next day.
This has been documented at devtest-lab-auto-shutdown
(If the reply was helpful please don't forget to upvote and/or Accept as Answer, thank you)