When may one remove Rashi tefillin and put on Rabbeinu Tam tefillin?

Greetings, 

Some have the practice of putting on Rabbeinu Tam tefillin after Aleinu l'shabeach, and studying Chok L'Yisrael and the like with them. Others have the practice of putting on Rabbeinu Tam Tefillin before Kedushah and Uva L'Tzion, so that they may recite one Kedushah with them. This is the proper practice. However, all this applies only when the entire congregation is waiting to put on tefillin before Ashrei. But an individual praying with the congregation, if by pausing before Ashrei in order to put on Rabbeinu Tam tefillin he will forfeit reciting Kedushah and Uva L'Tzion with the congregation, in such a case it is proper to put on Rabbeinu Tam tefillin after the prayer (Kitzur Shulchan Aruch Yalkut Yosef, siman 34, se'if 7). 

With blessings, Hillel Meirs