Is に required after 後？


"I moved two years ago" would be 二年前に引っ越した I think, but if I want to say after
x time, would I use に？E.g. 四日後に, or is it not required?




In your examples, に is optional both after `～前【まえ】` and `～後【ご】`. You can drop
に and say 2年前引っ越した and 2年後引っ越すつもりです, although these sound relatively informal.

Note that when these words mean "before/after ～" rather than "～ ago/later",
the particle choice may be more tricky. See: [後で vs. 前に- Why not the same
particle?](https://japanese.stackexchange.com/q/16269/5010) and [What's the
difference between に and で when speaking of time of an
action?](https://japanese.stackexchange.com/q/685)

