In the ZBX-2852 Richlv recommends to create separate issue. So, created.

I want to note that without reading the documentation to understand the interface that is that it is impossible!
http://www.zabbix.com/documentation/1.8/manual/config/screens_and_slide_shows

It can be easily confused (that above privacy for me and has happened).
It is suggested that like to do something like this:

Rename the "Update interval (in sec)" to the "Default slides change interval (in sec)"
Rename the "Delay" to the "Individual delay"

In tabular form need to unify the notion: "Delay" change to "Default slides change interval". !!!!

Documentation should be noted that the interval less than 5 seconds will be counted as 5 seconds.

Additionally i propose to improve GUI usability.
If "Individual delay" is set to '0' for a slide, then is slide-show editing form in column "Individual delay" should be displayed simply text "default" instead of "0".
If user tried to edit a slide, then should be checkbox "Individual delay" and if is checked then input field for value (seconds) should be visible.
So it will be totally intuitive, even without reading the documentation.

It would also be good to check whether the user has not entered a value less than 5 seconds.

Also note that the documentation now has inconsistence: http://www.zabbix.com/documentation/1.8/manual/about/what_s_new_1.8.3?do=show#improved_slideshow_refresh_rate_selector
You like this?: refresh time multiplier <> refresh (what_s_new_1.8.3) <> Update interval <-> Delay