Why did my delivery date get changed from 03/03 to pending for my tax refund

It seems you were given an estimated date. Never go by estimated dates. This is just a projection date based on the assumption that the IRS will process your return within the regular 21 days timeframe. 

When you receive a notification from TurboTax that your return has been “Accepted” it means that the IRS has accepted it for processing. It does not mean that it has been processed yet, just that is complete and accurate for them to start working on processing your return. You might also get a message for estimated processing time. This is just an estimate, since TurboTax has no control over when the IRS or any state will process your return, once they have been “accepted” by them.
 

The IRS issues most refunds within 21 days, assuming that there is no delay and nothing is holding your return. Some returns are subject to an automatic hold due to the Path Act when certain credits are claimed. 

The (PATH Act) prevents the IRS from issuing early refunds (before mid-February) on any tax return that claims the Earned Income Tax Credit (EIC) and/or Additional Child Tax Credit. For more information click on the link below
 

When will I get my refund if I claimed the Earned Income Tax Credit or Additional Child Tax Credit?
 

You can also monitor your refund status by clicking on the link below 

To track your Federal Refund 

Where's my Refund

To track your State Refund 

How do I track my state's refund?