When do colleges call after the CAT result?

After the declaration of the CAT Result, the admission process will be conducted by the 19 IIMs and more than 100 B-schools across India. 

Once the CAT result is declared, the IIMs and other participating institutes declare the shortlist of candidates on the basis of the CAT cutoff. The second step of the CAT Selection Procedure will start after this.

So applications for colleges will start after the CAT results are announced.