Issues
1/ Content Edit Page – Show mm/dd/yyyy

2/ Content Listing Page – Show unknown (AM / PM) time

What I did to resolve it?
1/ Add a new ViewMap Control
Advanced Settings → Controls → ViewMap → <Create new>
HostType: Telerik.Sitefinity.Web.UI.Fields.DateField, Telerik.Sitefinity
Layout: ~/Utils/Extensions/DateFieldExtended.ascx
Sample: DateFieldExtended.ascx (github.com)
2/ Update Content Type Listing DateTime Format
Advanced Setting → DynamicModules → Controls → <Custom Module Backend Definition> → Views → <Module Backend List> → View Modes → Grid → Columns → <Field> → Client Template →
<span>{{ (Start) ? Start.sitefinityLocaleFormat(‘dd/MM/yyyy hh:mm tt’): ‘-‘ }}</span>
Do for LastModified, DateCreated fields too.
Resolved Screen
Content Edit Screen

Content Listing Screen

References: