At the max 2 minutes should be alootted to each question in Jeemain as 90 questions there with 180 minutes.

Dont focus too long on one problem if its difficult you can simply move ahead. 

You can also save time on easier questions and use renainder time for tougher questions at last as and when you have time. 

For baords questions are unequal in size so no specific time. Secondly difficulty and question sets different for all baords and subjects so this you can determine by solving only previous year papers.