When to send Change the Dates

We just decided to postpone from May this year to May of next year. We sent out Save the Dates back in October. I'm not sure when do send new Change the Dates, do I send them next month when we would have sent invitations? Do I wait and send them on a normal Save the Date timeline and just field questions for now? I didn't anticipate having to postpone so I'm not sure what to do here.