'Confirming Vendors'

So this is on EVERY timeline and check off sheet I read.

Does that mean I have to call every vendor I'm using to check that they can still do everything they said? lol

When should I be making these phone calls?

Do I have to call all these places:
Hall, church, RD location, florist, DJ, photo/video, limo, shuttle, hotel, salon, bakery, tux place??