Getting last 6 months of data from today's date in a REST api call

My question:
I’m using PM to test out Sharepoint REST apis and need a call that GETs all news posts first published in the last 6 months. The “firstpublisheddate” field is a date field, so I need a filter like:
firstpublisheddate ge today minus 183 days.
Can I use the {{$timestamp}} variable to get today’s date and if so how would I reflect the last 6 months?
Or should I use “moment” as mentioned in the below question with a .subtract(183, ‘days’)?