Why iPhone asks me to change password within 59 minutes?

Passcode and password are 2 different thing.

Passcode is for locking your screen and screen time.

Password is for you Apple ID.

You can change Apple ID password here => Change your Apple ID password - Apple Support

Best you enable 2 factor authentication to protect your Apple ID, see here => Two-factor authentication for Apple ID - Apple Support

Note: Enable at least 2 trusted phone numbers, landline can also be used.

Unless you have a company iPhone which requires you to change the password regularly.

It's a scam.

Are these calendar notifications?

Axel F.

Do you have a work email account on your iPhone?

That would be why, talk to your IT support people at your work.