It is very doubtful that a Buyer you are working with becomes unresponsive to the milestones. Yet, if such a situation takes place, we will constantly send alerts to the buyer to respond. We will wait for 9 days for the buyer to respond with regular alerts. If the buyer responds within 9 days, it's just the thing. However, if the buyer doesn't respond at all within 9 days, you will receive your payment and you can initiate the next milestone.