I have a published web map with time enabled on the hosted feature layers. A web app was created of the Web AppBuilder (using the configurable Jewelry Box Theme and the Time widget). I noticed the timeline bar did not behave as the underlying web map. The hosted feature layers have four day data (datetime in UTC). There were only 3 time slices on the bar on the web app while the web map showed 4 slices correctly.
(attribute tables for the underlying feature layers)
(timeline on the web map showed four time slices on the bar correctly)
(timeline widget showed only three slices incorrectly)
An interesting thing is when tested using a configurable template (Time) it behaved in the same way as the web map.
I have also posted the same question to the ArcGIS Online forum and was instructed to repost it for the Web AppBuilder team to look into.
The web map is http://arcg.is/1GHbaD
The web app made from hte web map is http://arcg.is/1vC5zm