Is it time already? = もう時間なの？
Is this it for today? = 今日はもうおしまい？
どちらも「もう終わっちゃうの？」という気持ちが伝わると思います。
そして、I enjoyed your lesson. (あなたのレッスン、楽しかったです。）とか I learned a lot today. (今日、色々勉強になりました。）とか加えるといいと思います。
最後はもちろん Thank you! です。
That lesson just flashed by! So useful and a lot of fun, thanks!
In this phrase you firstly express your surprise that the lesson 'flashed by' so quickly. When involved in deep conversation or concentrating on dialogue or an article, the minutes may tick by surprisingly fast. Secondly you compliment the teacher on working with you with such 'useful' material. Thirdly, you say, "Thanks!"
The time just flew by, I had so much fun and learned a lot
Wow that went quickly, I enjoyed the lesson and it was very informative
If time flew by it means it went very quickly. There is a common expression in English which is "Time flies when you are having fun"
E.g. My holiday just flew by. I can hardly believe it is time to go back to work tomorrow
If time flew by とは、時間が過ぎ去るのが早いときに使える表現です。
英語でもっと一般的な言い方は"Time flies when you are having fun"などがあります。
E.g. My holiday just flew by. I can hardly believe it is time to go back to work tomorrow
例：楽しい休暇も一瞬だった。明日から仕事とか信じられないや。
Wow that lesson flew by. Thank you for making it fun and informative.
Time flies in your lessons, that lesson was really fun!
This lesson went so quickly, it was so much fun.
"Time flew by" or "time flies" is simply saying that the time went really quickly and can be used in many contexts. I think that if you think the lesson is fun it is always nice to say "thank you" and then adding on "it was so much fun" is a nice thing to add on the end to say what you thought of the lesson. You could change "fun" for "enjoyable" to mix it up!
"time flew by" または "time flies" は「時間があっという間だった」という意味で、いろいろな文脈で使われます。
レッスンが楽しかったと思ったときは、"thank you" と感謝を伝えるといいと思います。それから最後に "it was so much fun"（すごく楽しかった）と感想を言ってもいいですね。バリエーションとして、"fun" を "enjoyable" に変えることもできます。
日本 
イギリス 
