how to manage estimates of release, not getting heck of it at all from long time,. specifically, for android app.

calculate how much time all the requirements need to be implemented. Double the amount of it and add 15% of that time on top of it.
And if you've got a asshole product manager and you want to be on the save side add another 30% of that time on top of it, because he will say that it takes too long and he will give you a tighter deadline. It's better to be save than sorry.

@heyheni thanks man will try this but some of times i am not asked for estimates but given deadline to complete in, without any calculation just on the basis of business urgency. what do u suggest in that case.