You should not have problems, setting or changing the values of PeriodStart, PeriodEnd and MinSelectionRange properties in code-behind, as long as you adhere to the correct precedence, mentioned in our help topic
In case you need additional help with that, please open a formal support ticket and send us a running test project, demonstrating the problem that you have, together with detailed information on reproduction steps and expected result.
All the best,
the Telerik team
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