It took a while to get used to Japan's culture, didn't it?
Even though you were able to get used to Japan's culture, it took a while, right?
ご質問ありがとうございます。
JUKIYAさんの英文「It took a while to get used to it, didn't it?」はそのまま大丈夫ですが、最初の「it」の代わりに具体的に伝えた方が良いと思います。例えば、（日本の）文化の話でしたら、「it」の「Japan's culture」に変更できます。
もう少し自然な言い方で「Even though you were able to get used to it, it took a while, right?」と言えます。
ご参考になれば幸いです。
It must have taken a bit of time to get used to it.
JUKIYAさんの英語んでも良いですし、次のようにも言えます。
ーI bet it took a while to become accustomed to it.
「それに慣れるのに時間がかかったでしょ」
I bet it took a while to ... で「…するのに時間がかかったでしょ」
to become accustomed to で「…に慣れる」
ーIt must have taken a bit of time to get used to it.
「それに慣れるのにちょっと時間がかかったに違いない」
It must have taken a bit of time to ... で「…に少し時間がかかったに違いない」
ご参考まで！
アメリカ合衆国 
カナダ 
