It'll probably be fine getting tickets on the day.
当日チケット買っても多分大丈夫だよ、は英語で
You can probably just get the tickets on the day.
もしくは
It'll probably be fine getting tickets on the day.
説明したい場合
It's not going to be crowded on the day you're going.
君が行く日は混んでいない。
And considering the hassle of having to change the departure time on the day if you do buy tickets beforehand, you're better off just buying them on the day.
そしてもし事前にチケットを買った場合、当日時間変更する事になったら手間がかかるから、
当日に買ったほうがいいよ。
ご参考になれば幸いです。