From Admin panel, go to Catalog → Product. Edit product you want set is new product.

In the basic settings panel, Click Advanced Pricing link

Advanced Pricing panel:

• Enter the number of the Special Price.
• Assign the active time including Special Price From Date and Special Price To Date. You can type manually or click on Calendar icon to choose the relevant date.
• Click Done button to close panel.
• Click Save button to save product.