There are two exams held on same day I.e jee main paper1 & paper2. If you want to do BTECH from NITS and IITs than you have to given first paper1 through which you will get NITS  and than jee advance through which you will get IITs. If you want to do B.Arch from NITS than you have to given paper 2 which is only for getting admission into NITS not for IITs. If you want to do B.Arch from IITS (only 2 IITS have this program) than you have to given paper1 I.e jee main & also jee advanced if you clear both than Architecture registration will be start after declaration of jee advance result. You have to give preference for appearing in AAT.if you dont choose the option to appear for AAT while registering for jee advance than you are not eligible for B.Arch . THE dates of online registration for 2018 for BArch in IITs:-

1. 10-11june 2018

Test date:- 14 June 2018

Result:- 18 June 2018

Seat Allotment:- 19 June 2018.

Everything for BArch in IITs done through jee advance you don't need any admit card for AAT paper . Jee advance admit card is okk. You have to give BArch as the  choice while filling the Choice seat online at jee advance portal.