BoUk

Unlike other plugins, where check for missed schedules is hooked into init action, which in return means, there’s an extra database call created anytime the site is loaded, this plugin creates separate recurring cron task to check for missed schedules.
Checks are happening every 5 minutes and in case there are found posts missing its schedule, they are automatically published. From the principle this solution requires a functional WordPress cron subsystem.

Snack Missed Schedule

Uses separate recurring cron task to check for missed schedules.

Jennifer Moss

When a visitor loads your site, this lightweight script checks to see if any scheduled posts have been missed. If so, it publishes them immediately.

Scheduled Post Trigger

I have used this plugin for a couple of years without any issues. Without it, WordPress misses posts all the time. I don't understand why this functionality isn't built into WordPress, but I am thankful for the developer.  

The Plugin We Really Shouldn't Need

Checks to see if any scheduled posts have been missed. If so, it publishes them. NOTE: This plugin is meant as a stop-gap until you and your web host  …

Snack Missed Schedule vs Scheduled Post Trigger