Time limit for investment under section 54ec

Hi

Can someone please guide me what is the time limit to invest under section 54EC - is it 180 days or 6 calendar months?

My client has sold a property on 2nd Aug, if I go my end of 6 months the due date is 28th Feb and if I go my 180 days due date is 29th Jan and if I go layman way the due date is 1st Feb????

Please help its urgent