Yes, a teacher can snooze any Objective whether students have started it or not. If a student is playing in the Objective and it is snoozed, the next time the student signs in they will begin the next Objective and their progress in the snoozed Objective is saved.
Snoozed Objectives can be assigned to individual students and will appear in the Assignments area.
For more about snoozing - How can I skip (or snooze) some objectives for my students in the Journey?
For more about Assignments - How do I assign, edit, or reorder class and individual assignments?