Interactive video overlays triggering early on iphone

You may wish to edit your video to have a great blank space (margin of error) at the points where the overlays will go. This might account for the variability of the internet and various bandwidth issues. 

I have one client at the moment where all of the content will be delivered to mobiles, not desktops.  Trying to get consistent performance across all platforms can be a nightmare.  I'm not blaming Captivate though.  I see the issue as the way the different mobile OSs adhere to their own standards.  I have found that the more complicated you make your course content, the harder it becomes to get everything to work consistently. 

I know Captivate supports the idea of using overlay slides with videos, but if you are running into too many issues, you may simply need to rethink whether that feature is worth the trouble and budget you are burning on trying to implement it.  Another approach that involves breaking up the videos and then having the questions on their own slides between the videos might make more sense and allow you to sleep at night. 

By all means try another authoring app if you want.  But from what I hear, none of them can guarantee everything will work as you might want.  They all have limitations.