Once upon a time, I asked why they won't give timelines.  The reason is, if they say 7 days and it takes 8 days, then their customers are going to be mad.  Well, then give a cushion.  If you think it is going to be 7 days, then say 10 days to give a cushion (I know, giving a range of 7 to 10 days would be too complicated).  It's hard dealing with clients when you have to tell them, someday my software will be up to date and I will get your return done then.