You can return the book anytime, as long as it's before the
library closing time. Even for a 24-hour bookdrop, try to return it
before it closes. That is to prevent any technical problems (such
as book not properly scanned as returned, in which case you can be
fined for because the librarians can only check it next day).
If you can't finish the books in time, renew it. Or for cheapo
Singaporeans, return it, lurk around the library for a few hours,
then re-borrow it to prevent paying the 50 cents fine.
