Note: The Project must be in a State of Draft or Open to have new Schedules added.
If the Project status is Closed, the option to add a new schedule will not be available.
To add a new Schedule, change the Status back to Live for the Project (Project > Project Home > Overview tab).
Then Refresh your Schedules List for the + New option to show.
Your Profile (Resources > Profiles > Profile List) must also be set to allow to modify, not just view only. 