When you change the default layout or schedule new layouts to be displayed on your device.
The collection setting - it defines how often your device will connect to the CMS and look for new/updated files/schedule.
Once your device connect to the CMS and download all required files it should display content according to your schedule - unless your schedule is invalid of course.
What’s also important - layout duration, if you have some really long durations on your layout, it will delay any content change.