Is there any problem with tying Tzitzis at night?
No, it is fine to tie tzitzis at night.
Although the mitzvah of wearing tzitzis does not apply at night, there is no problem in tying (and thereby “forming”) the tzitzis at night.
The same is true for all mitzvos: It is permitted to bake matzos before Pesach, even though the mitzvah of eating them is only on Pesach; it is permitted to tie the Four Species together before the festival, although the mitzvah applies only later — and so on.
Best wishes for a chag kasher ve-same’ach.