僕は一月の二十五日までに図書館の本を返却しなければならない。

。

I have to return the library book by January 25th.

Literal

I [topic-は] January [possessive-の] twenty-fifth [by-までに] library [possessive-の] book [object-を] return must-[なければならない].

~までに ('by, no later than') marks a deadline — distinct from まで ('until'), which marks duration. 返却する (へんきゃく, 'to return [borrowed items]') is more formal than 返す. 図書館の本 ('library book').