ios - Query objects newer then 24 hours -

so way snapchat has, show in story images/videos newer 24 hours old. how can same using query code:

func querystory(){         let query = pfquery(classname: "myclass")         query.wherekey("ispending", equalto: false)         query.limit = 1000         query.orderbydescending("createdat")          query.findobjectsinbackgroundwithblock { (posts: [pfobject]?, error: nserror?) -> void in             if (error == nil){                 // success fetching objects                  post in posts! {                      if let imagefile = post["userfile"] as? pffile {                         self.userfile.append(post["userfile"] as! pffile)                         self.objid.append(post.objectid!)                         self.createdat.append(post.createdat!)                     }                 }             }             else{                 print(error)             }         }     } } 

i tried adding:

var date: nsdate = nsdate(timeintervalsincenow: -172800) query.wherekey("createdat", greaterthan: date) 

but gave me 0 items.(my class has total 28 items). ideas?

the correct format 24 hours be:

let date: nsdate = nsdate(timeintervalsincenow: -86400) query.wherekey("createdat", greaterthan: date) 

how old files trying query parse?