The trial version of Kendo UI does not have a time bomb which prevents its usage when the 30 day trial lapses. However, if you continue to use the trial after this period expires, you directly violate the trial EULA that you agreed with when you downloaded it.
Therefore, when the trial evaluation timeframe ends you should either make a purchase or continue using the Kendo UI Web GPLv3 version (if applicable for your project).
the Telerik team
Join us on our journey to create the world's most complete HTML 5 UI Framework - download Kendo UI