Hello @Protect-Preserve ,
Generally if you're running into some basic connectivity issues, you can easily resolve them by clearing your cache or resetting your router (late night upload latency can cause issues with running some elements of our site, since it tends to be more data-intensive then other sites).
With that said, we've also received some reports about the legacy editor (which you still use) having issues functioning at night. This can include editing/saving legacy emails, scheduling the legacy emails, and them actually sending out. Our engineers are aware of this, and are looking into it. However, since the legacy editor has been getting retired in waves since the release of our current mobile-compatible editor in 2017, they're strongly suggesting anyone running into these issues to make the switch to the current editor.