By default password will expire in 90 days and app will not allow user to sign-in and will show error message
PASSWORD_EXPIRED
It is possible to change (reduce/increase ) the time after which the time of the reset password link expires
In the Admin Panel :
Go to System -> Configuration Advanced -> Admin -> Security and change Password Lifetime (days) and Password Change fields.
Reference:
https://github.com/GoogleCloudPlatform/fda-mystudies/issues/2645
https://stackoverflow.com/questions/19293020/change-time-of-expiration-for-reset-password-link-in-magento-back-end
https://stackoverflow.com/questions/38743317/magento-stuck-on-its-time-to-change-your-password
https://magento.stackexchange.com/questions/231387/how-to-change-default-magento-admin-password-expiration-period