I Think these rules will work.
Junior : above 5 merit
Member : Above 80 Merit
Full Member: Above 220 Merit
Senior : Above 450 Merit
Where is the hero? They don't need to be legendary?
May be @MFahad By mistake, Hero Member has excluded members. @yahoo62278 sir mentioned that only junior member can give merit countdown here if less than 25 merit in case of all other members.
Junior member 5+-----9
Member 75+----99
Full member 225+----249
Sr member 475+----499
Hero member 975+---999
But the interesting thing is that there is no need to give merit countdown for those who will be able to score 75+,225+,475+,975+ merit without countdown.They can change rank already.