Two definitions straight from the Oxfordcitionaries
pastime (n) - An activity that someone does regularly for enjoyment rather than work; a hobby.
timepass (n) - The action or fact of passing the time, typically in an aimless or unproductive way.
The latter word is Indian English. Though the dictionary has not mentioned this word as a verb, here, it's common to say (though in an informal way) "Don't timepass, the work has to be finished in an hour."
What if I want to refer pastime as timepass and timepass as pastime. In other words, what if I want to ask a native speaker that how does s/he passes her time (timepass) and an Indian about how does s/he does pastime?
An example for the native speakers on timepass:
"Narendra, why are you throwing stones in the river?" ~ "Ah, I'm waiting for my friend. She hasn't come yet."
"And throwing stones?" ~ "Just simply... timepass."
Here, by no means timepass is done for enjoyment. Nor is it a hobby.
Note: To most of Indians, pastime is actually timepass. Because if you ask about pastime, you are very likely to get an answer about timepass.