Good info raihaan. The duration option should be removed from the plugin. We are an existing customer, and have used the feature in the past so it looks like it should still work (but doesn't for a new pipeline).
Define a duration for your Spot Instances
Spot Instances with a defined duration (also known as Spot blocks) are no longer available to new customers from July 1, 2021. For customers who have previously used the feature, we will continue to support Spot Instances with a defined duration until December 31, 2022.