Why isn't my date related (start/end) option work correctly?

There are options at your  slides to publish/unpublish them, and also event related dynamic slide generators are having started/ended options to only show specific events, which for example haven't ended yet. Most of these options are using this date setting to figure out what is your current time:

WordPress

In WordPress we are using the Settings -> General -> Timezone given time. 

Joomla

In Joomla we are using the System -> Global Configuration -> Server -> Server time zone given time.

WordPress & Joomla - Misunderstanding dynamic slides

The problem could also be just a misunderstanding of how dynamic slides should work. Dynamic slides are only checking, wether or not your slide should be in the slider, after the  cache expiration time has ended. You could change this value to 0 hours to have immediate result, just that is not so optimized, and we would rather suggest having this value on at least 1 hour. Or manually refresh the generator's cache and leave the cache expiration time as it is.

WordPress & Joomla - Plugin/Extension

Some of the plugins or extensions of our dynamic slide generators are offering they own time options, so if your framework specific time doesn't solve your issue, you should check out your plugin's/extension's global settings, in case it has a "timezone" or some similar option.