lorentz law

say an object of mass "m" who's has a constant acceleration "a" (in it's point of view)
In the point of view of the object "t" time has passed
Let's say it started immobile in a referential A

how would you calculate the time passed in the point of view of referential A

Sorry for the horrible English but it's not my native langage.  

Assuming a constant accel int the rockets frame:
t'=y(t-(v/c^2)*x ), v=at, t' is in frame A
Also note: It's mass dosen't matter for this question unless this is a rocket in which case m changes and I don't care.