When you set a loan period all catalogued resources will default to this loan period. Most schools set this as 365 days and then rely on the Loan Cut-off dates to ensure the due date is at an appropriate date at the end of each school year.
Due dates for Textbooks are difficulat to manage. We are considering End of Term dates that would allow you to quickly assign a due date to loans... if you'd like to see this let us know!
If you do set this as 365 days, make sure you go into Loan Cut-off dates and set a cut-off date for each year level of students and also for staff!