Hello. My son is doing MS in Astronomy & Astrophysics ( Dual degree 5 years ) he has learned Engineering Physics for the first 3 years and 4th year onwards he has choosen MS in Astronomy & Astrophysic

Hello. 

My son is doing MS in Astronomy & Astrophysics ( Dual degree 5 years ) he has learned Engineering Physics for the first 3 years and 4th year onwards he has choosen MS in Astronomy & Astrophysics in an Indian College, My quetion is is writing Thesis tough, can he complete his Master degree in one go or he need more years to complete it ? I am bit confused about it so need your sggetion on the matter 

Thank you in advance