Odoo-Tutorial/library/data/library_cron.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>

    <record id="cron_update_book_update" model="ir.cron">
        <field name="name">Update Overdue Book Status</field>
        <field name="model_id" ref="model_library_book" />
        <field name="interval_number">1</field>
        <field name="interval_type">days</field>
        <!-- <field name="number_of_calls">-1</field> -->
        <field name="state">code</field>
        <field name="code">update_book_status()</field>
        <field name="active" eval="True" />
    </record>

</odoo>