They helpfully note:
You will be able to browse the shelves and renew and check out material. The bookdrop will be accessible as usual.Browse the shelves? There's two dozen library branches! What kind of upgrade requires 72 hours to complete?
Items will not become due during the week of June 19 - June 25. The Library encourages you to return your Library material later that week.
(I'm sort of hoping that after this the "find this book at my library" Amazon bookmarklet will work; the iPac version of that bookmarklet was for a different version of iPac than the Ottawa library was using.)