1.8 Alpha2 API Stats - Date Format

On the 1.8 Alpha2 API, when sending fromDt and toDt, what format should they be in?

2016-12-31 or 2016-12-31 23:59:59

They should be in Y-m-d H:i:s format - i.e. 2016-12-31 23:59:59

Thank You. 20 Chars.