Time management is very much important in IIT JAM. The eduncle test series for IIT JAM Mathematical Statistics helped me a lot in this portion. I am very thankful to the test series I bought from eduncle.
Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Saurabh 1
If I have to go for any one of them I would have surely considered the first one by Ausaf sayeed cuz it's a good book which cover some important theoretical aspects of each topic and have ample of questions pertaining to specific topics. Ausaf sayeed has tried to give blend of easy to difficult questions where you can even solve questions from oil india, gsi as well. Overall it's a good book.