New messages posted within last week

Is there way to retrieve new/unread messages which were posted within previous week?

I can use ?rangeTime=1w parameter in /search/messages/count request. But how can I detect if these messages are new or not? 

From other side I can use /restapi/vc/boards/id/{board_id}/messages/read/count and /restapi/vc/boards/id/{board_id}/messages/count requests and calculate difference to obtain number of unread messages. But how can I identify rangeTime or post_time here?

Thanks