Hi Zak,

you can add a scheduled action like this, this may already defined in the link.

In the XML,

<record id="ir_cron_scheduler_demo_action" model="ir.cron">
    <field name="name">SMS Reminder</field>
    <field name="user_id" ref="base.user_root"/>
    <field name="interval_number">2</field>
    <field name="interval_type">minutes</field>
    <field name="numbercall">-1</field>
    <field eval="False" name="doall"/>
    <field eval="'sale.order'" name="model"/>
    <field eval="'rental_sms_reminder'" name="function"/>
</record>

Then in the Python,

class SendSMS(models.Model):
    _inherit = 'sale.order'

    @api.multi
    def rental_sms_reminder(self):
        #write Function body here

Settings -> Technical -> Automation -> Scheduled Action,  select the new scheduled action , here 'sms reminder' , open it in the form view, then click on Run Manually to check its working

Add a print in the function and make sure that the function get called. Thanks

@Niyas can you send me a link for a small automated Action project, to run it and see how i should define my automated action. thanks 

Thank you Niyas you helped me so much :)