Was at Amazon today and noticed when I added an item to my cart, it immediately took like 10% off of my order total but said the 10% offer was only good for so many minutes and then the offer would end. Does anybody know of a Magento module that does this? Would be nice to also run it after hours to encourage more sales.
You may be looking at Cart Price Rule. According to official document:
Cart price rules apply discounts to items in the shopping cart, based on a set of conditions
This rule will only show on the cart page, and you can set start date and end date on the rule.