how to use javascript setTimeout function in firebase cloud functions

You'll need to wrap your setTimeout in a Promise:

exports.delayqueue = functions.database.ref('/queues/{queueid}/members/{memberid}').onWrite(event => {
  var members = event.data.ref.parent;
  var user = event.data;
  var queueid = members.parent;
  var userid = event.params.memberid;
  var delayfor = user.child('delay').val();
  var name = user.child('name').val();

  if (delayfor !== 0){
    members.child(event.params.memberid).remove();
    return join(userid,queueid,delayfor,name);
  } else {
    return;
  }
});

function join(userid,queueid,delayfor,name){
  return new Promise((resolve, reject) => {
    setTimeout(function(){
      var ref = db.ref("queues/queueid/members/userid");
      ref.set({
        name: name,
        timestamp: Date.now(),
        delay : 0
      }).then(resolve, reject);
    }, delayfor*1000);
  });
};

Note that the time spent waiting for setTimeout is billed as function execution time and is also subject to the function timeout. If you're only delaying a few seconds, that might be okay, but if the delay is expected to be minutes this solution isn't going to be viable or cost-effective.