Schedule condition or start condition in actions

Hi All,

I have a requirement to create an action profile to a Contract in CRM in such a way that before the contract expires  Contract in CRM in such a way that before the contract expires  i mean just 1 week in advance an alert should be sent to sales rep. For this i have created a date profile and date type.

But I am confused whether to use Start Condition or scheduling condition

If i use start condition then how should i schedule the action or is it not required?

Regards,

V rao