Why is it not permissible to don tefillin at night? In the verses commanding us to place tefillin, there seems to be nothing to indicate it is a time-bound commandment to the day only, as with tzitzit, which specifies, ’u’raitem oto’. If it is the issue of delcaring a bracha unnecessarily, can we not just say a bracha without ’shem u malchut’?

There is no Isur from the Torah in donning Tefilin at night. The Mishna Berura writes that we don't don Tefilin at night because we might fall asleep and then cause the Tefilin to be desecrated. Rabbi Yitzchak Grinblat