On Mivtzaim, may one put on just the Shel Yad or Shel Rosh if the person will not have time to wear both Tefillin, or does not want to do so?[1] Yes. [1] Based on Admur 26:3
On Mivtzaim, may one put on just the Shel Yad or Shel Rosh if the person will not have time to wear both Tefillin, or does not want to do so?[1]