How to add special price to Extended Product Grid in magento?

Please open Extended Product Grid settings (Grid Attribute Columns) and enable the special price.

If this does not help, open file (if you have one)
app/code/community/Symmetrics/DeliveryTime/Block/Adminhtml/Catalog/Product/Grid.php and replace

extends Mage_Adminhtml_Block_Catalog_Product_Grid

with

extends Amasty_Pgrid_Block_Adminhtml_Catalog_Product_Grid