I haven't applied yet, but from what I understand I don't think that they will ask very different things for the LORs. After all, your recommenders will probably send their letters to more than one institution, and I doubt they have the time to write a different letter for every institution.
I read that it would be ideal if you could give your recommenders plenty of time, maybe try a month or two before your intended submission date. It would also be helpful if you could give them some materials, such as your CV, draft of the SOP, maybe some ideas on what they could touch on, etc.
Here is a website I've seen linked on gradcafe a few times that could come in handy, it has a section on LORs: https://sites.google.com/site/gradappadvice/letters-of-recommendation