Make 2 columns in a table, lastLogin and lockout, then Just write the last login date into a table column, and when they logout, flip the bit in the lockout column to 1.
Then when they login, if the lockout bit is 1, calculate the next available date to login, if it's the next day, unlock them and let them login.
[Edit]
you might need this to unlock the account
UPDATE CustomerInfo Set Lockout = 0 WHERE AccountName=@AccountName AND DATEDIFF(hour, LastLogin, GetDate()) > 0"