It is definitely not time to wean. They are far too young. The average weaning age for an IRN is between 10 and 12 weeks. How many feedings are you giving them and how much formula per feeding? Do you have a gram scale? Weighing them every morning is necessary so you know if they are keeping their weight on. Weight loss is the first indication that something is wrong. They should only lose weight when they fledge. Right now they should be gaining daily.
You also want to check the consistency of your formula. Different aged chicks want different consistencies. The older the chick, the thicker the formula should be.
You want to abundance wean them which means that they have a variety of foods available to them at all times and they continue to be hand fed until they are ready to stop.
Also, you are feeding the formula too cool. Up the temperature to between 107 and 110 (never over 110) and see if that helps. Sometimes birds won't accept formula that is too cool. They also may not accept a hand feeding based on technique. Make sure you calibrate your thermometer first just to be safe.
Did the breeder give you a demonstration or have you hand fed before?
Here is a really comprehensive article on hand feeding that should be helpful to you. It explains proper technique and temperature and weaning ages etc.
http://www.theparrotuniversity.com/arthandfeeding2.php