Using API V1 to get the most popular topics in the last 6 months

Hi, 

I use the following code to retrieve the most viewed Threads in our community:

<#assign popularPostResult = rest("/categories/id/${categoryId}/search/messages?q=is_root:true&sort_by=-views&restapi.response_style=view&page_size=1000&page=1").messages.message />

The results are sorted by most viewed.

How do I get the most viewed threads for only the last 6 Months? 

If you have any links to documentation it would be great as well.

Regards

Kallie