Neb. Rev. Stat. § 76-2,102

Neither possibilities of reverter nor rights of entry or reentry for breach of condition subsequent, whether heretofore or hereafter created, where the condition has not been broken shall be valid for a longer period than thirty years from the date of the creation of the condition or possibility of reverter. If such a possibility of reverter or right of entry or reentry is created to endure for a longer period than thirty years, it shall be valid for thirty years.