Time is a measure of events that happened, happening and going to happen.Time Travels only in one direction and we cannot stop the the time.

Time Travel is a big word and a real thing but not as portrayed in movies.Following certain conditions you can time travel.Many Hindu Text and Scientist have talked about the same.

Ronald Lawrence Mallett is know as father of time travel.He argued using general relativity  time travel is possible in 21st century.

Albert Einstein was the first person to realize that time is not constant but instead slows down as you move faster through space.He mentioned rate at which time passes depends on observer frame of reference. 

Stephen Hawking once stated that time travel is not possible.In fact he had a party hosted for time travelers.He had 3 Theories of Time.First one Thermodynamic arrow time as we can see a glass falls and broken in to pieces but cannot see the same pieces combining to complete a glass all by themselves.Second comes Psychological arrow time according to which time travels only in one direction that's we can remember the past but not future.Third comes Cosmological arrow time In which he says universe is expanding rather than contracting

Hindu Text, The text tells us about some characters who have time traveled.King Kakudmi with his daughter Revati traveled to a different  world when he came back to earth found everything was aged, generations were passed. Multiple Universe theories are mentioned in Purana's and Vedas.In the story of Mahakaal the lord Shiva and Sati travels to future to test lord Rama.Even though we could find some carvings in Hindu temple related to time travelers , No text mentions about the people traveling to past but rather in extreme circumstances the Kala Chakra or cycle of time is reversed.

Time Paradox, In which a person makes time machine travels to past and the paradox that if kills his grandfather then his father will not be born and then no chance that he is born which means he would not exist in future and therefore he can not travel to past.

However According to few of my understanding time can be still classified but these are just assumptions.Firstly Consciousness of the time which means when a person walks 2 hours in a desert looking for water which makes him feel hours like a day and the same person watching a movie for 2 hours ,once it ends he feels the hour lesser, than he spent.Secondly Species of time according to this Time for species differ, When for a human it is  24hours but for a Mayfly it is a life time.Third comes Wandering time as per this after death our soul may wander around the past life or space at different point of time just like a ghost.This happens may be because god wants us to walk through our past life and regret for our bad doings.

However Humans using advanced technology and certain methods they may be able to travel faster than the speed of light or travel backward in time only movies.Einstein Rosen bridges proposed wormholes would appear identical to black holes but matter which entered it would be relocated to a different location in space time.However most of the physicists agree that traveling at the speed of light and backward in time is not possible.Hawking provides more formal explanation on same.