The reference page for the getMore command in 3.2 includes the following documentation for the maxTimeMS field:

maxTimeMS | positive integer | Optional. The timeout duration in milliseconds.

This is accurate, but incomplete. The maxTimeMS field is only legal for getMore on awaitData cursors. An error will be returned to the user if maxTimeMS is attached to a getMore command on a non-capped, non-tailable, or non-awaitData cursor. Furthermore, the timeout is not used to throw an error if the operation exceeds its allotted time; instead, the timeout is the amount of time for which the getMore operation will block waiting for new data to be inserted into the capped collection.