Can your manager change your work hours without verbally informing you?

Yes, is the short answer. The manager can put a roster notice on a board with changed work hours on it, without telling you verbally. There are also many other ways of notifying you.

It is usually reasonable for a manager to change work hours to suit the organization. Usually the manager in the interests of a happy workforce will try to fit in with workers' preferences but it is not always possible.

Similarly, the manager may notify you in various ways. By letter, by a roster notice on a board, by email, by a message left on your phone or voicemail or to someone at your home.

If the manager has given you enough notice of the change then there is probably not a lot you can do about it. If you did not get a verbal notice but you did get another notice which you didn't know about, then there is a problem with communication that you have to sort out with your manager.