server-tools/letsencrypt/data/ir_cron.xml

<?xml version="1.0" encoding="UTF-8"?>
<openerp>
    <data noupdate="1">
        <record id="cronjob" model="ir.cron">
            <field name="name">Update letsencrypt certificates</field>
            <field name="model_id" ref="model_letsencrypt"/>
            <field name="state">code</field>
            <field name="code">model.cron()</field>
            <field name="interval_number">11</field>
            <field name="interval_type">weeks</field>
            <field name="numbercall">-1</field>
        </record>
    </data>
</openerp>