Like you properly pointed out you can edit the ContentViewSingleitemView template and add a code-behind or inline logic that will compare the values for EventStart and EventEnd. You can then map the external template globally by following the instructions we've provided in this blog post
. Please do not hesitate to get back to us if you need some further clarifications or have any additional questions.
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items