Question

while crossing the IDL a person will have to add one day while travelling from

Answer 1

The date changes backwards. You don’t really gain time. I have frequently flown from Sydney to Los Angeles. The flight left at 16:00 or so, and arrived in Los Angeles about 10:00 the following morning, which however had the same date. That’s one way to have a 40 hour day.

Answer 2

While crossing the IDL a person will have to add one day while travelling from WEST TO EAST.