As an organization, we're being asked constantly how the USPS' Network Optimization Plan is going to effect their mail deliveries. Mail-tracking combined with predictability is the key.
Thankfully the USPS has made a Service Level Map available that should provide that predictability. The link below will allow you to gain a better understanding on transit times and hopefully provide more stability in your marketing campaigns.
From the US Postal Service:
Service Standards maps and data files containing originating, destinating, and destination entry data files have been added to the Modern Service Standards page on RIBBS®. The maps reflect service standards for market dominant (Mailing Services) products that are effective as of July 1, 2012.
A Service Standard represents the level of service that the USPS strives to provide to customers. These standards are one of the primary operational goals and provide benchmarks against which we measure service performance success.