When can a visitor sign-out?

Here are information and system rules regarding visitor sign-out for Zipline:

• A visitor can only sign out if they are currently signed in
• Visitors can only sign out within 4 hours of their scheduled booking start time (regardless of their physical sign-in time)
• Visitors are not required to sign-out to be able to sign-in again
  • as long as the previous sign-in time was more than x hours ago