May someone who is not accustomed to laying tefillin practice binding at night, when there is no mitzvah, so that they will be proficient at wrapping when the day comes?
This is an interesting but difficult question. It is not addressed explicitly anywhere I looked and I assume it is because it is quite theoretical. Someone learning can wait to practice by day. But still interesting.
As mentioned in the comments the mitsva of tfilin deoraita applies during both day and night. The reason Hazal forbid putting on tfilin at night is because one cannot sleep [or pass gas] wearing them (Shulchan Aruch OC 30:2). Even if these reasons do not apply to your case, we do not "double guess" Hazal when they forbid something even if their rationale doesn't apply.
On the other side, the same siman of Shulchan Aruch says we can leave tfilin on if one wears them before the sun sets. The next one says one can put them on before daybreak and touch them when the sun rises to say the bracha.
Also when a minor needs to learn, there are certain barriers which are lifted, e.g., saying God's name, which is allowed to teach a minor.
From all these I believe one can be lenient. But as always in these cases CYLOR.
PS. Note that this source mentions kabalistic reasons from the Arizal not to put tfilin on at night
Wear them in a way that does not comply with the mitzvah. Such as over a shirt sleeve.