In order to ensure your Campaign Items are being associated with the correct, valid Ad Price for their runtime. We have created a validation which ensures that the Campaign Item runtime is within the validity range set on Ad Price level. If you wish to create items which overlap on Ad Prices, the please create the following feature setting to disable the Ad Price validation on the until field which was included in version 2.118.
Navigate to Feature settings and create a feature setting with the following information:
Feature Setting Name: DisableAdPriceValidationUntil
Feature Name: MediaConfiguration