I hear a lot about the uptime of cobol/mainframe based applications, but the entire Commonwealth Bank ATM and eftpos systems used to go down for an hour or two

I hear a lot about the uptime of cobol/mainframe based applications, but the entire Commonwealth Bank ATM and eftpos systems used to go down for an hour or two at 3AM every Sunday, back in the day this was nightclub close and time for a kebab and caught me out quite a few times. It's been much better since they migrated.