account_invoice_calendar_event_eiru/account_invoice.xml

<?xml version="1.0" encoding="UTF-8"?>
<openerp>
    <data>
        <record id="view_order_invoice_form" model="ir.ui.view">
            <field name="model">account.invoice</field>
            <field name="inherit_id" ref="account.invoice_form" />
            <field name="arch" type="xml">
                <xpath expr="//notebook" position="inside">
                    <page name="account_invoice_calendar_event" string="Reclamos de cobro">
                        <field name="calendar_event_ids" context="{'default_partner_ids': message_follower_ids, 'default_name': name, 'default_start_datetime': time.strftime('%Y-%m-%d %H:00:00'), 'default_stop_datetime': time.strftime('%Y-%m-%d %H:00:00')}" />
                    </page>
                </xpath>
            </field>
        </record>
    </data>
</openerp>