when call start coming for WAT/PI from different MBA colleges who takes CAT score into consideration?

It totally depends on college to college. First of all, after you need to fill up the application form and then with small fees you need to apply in every college excepts IIMs in which you are interested to pursue your MBA degree before the college's application deadline gets closed. After this only if you fulfil all the eligibility and ends up in the college's first merit list then you will be called for the second round of WSAT and interview.

If you talk about IIMs so their interview procedure starts from late January and continue till March. Almost all the MBA colleges open up their new session in the month of June/July and their application deadline is generally till the month of February/March so generally, this second round procedure starts in the month of March.

But as I told you earlier there is no fixed timeline it totally depends on college when their application deadline finishes and they start their procedure. So you can check out the deadline of the colleges in which you have applied and estimate the procedure to be started after a week or two. Even some of the colleges have fixed date of the second round procedure so you can check out this thing even on the websites or their brochures.

All the best!!