I would like to know if it's possible to make a post field required based on a condition. For example if the users has selected that a "strategy" is of type "smart" from a radio button then the start and end date of the strategy should be required otherwise not.
In order to understand the context of the useage can you let me know if you're populating the fields on the backend or on the frontend ? Meaning are you using our Toolset forms plugin to create the posts?
In a case like this then you will need to use custom code to achieve. Unfortunately the code required to make this field required based on the conditions defined would be out of the scope of our support forum since we don't have any validation hooks that would apply to the backend.
On the frontend this would be something that would be possible to do with our Forms validation Hook but on the backend it would require the use of the wordpress default API functions to craft a solution.