Sonatype Support's hours of operation are from 8a.m. to 8.p.m Eastern time. Support outside of those hours is done on a best effort basis.
However, if you have purchased 24x7 support you can obtain round the clock support for critical system failures. To obtain out of hours support you must file a support ticket at https://support.sonatype.com using one of your designated support accounts, and select "critical production system outage" as the issue type.