You can email members of your group at any time. If you have a paid plan, you can send text messages to those in your group who have opted in to receive them.
To send a message, log into the site. From your account Sign Ups page, you can click on the Messages icon to the left to compose and send an email or text. You can also go straight to your sign up, and in the Admin Toolbar at the top, select Send a Message. From there you'll see the option to Email People Participating in a Sign Up. You’ll have options to message your entire group, specific individuals or those who have signed up or have not signed up.