WIOO is a "daytimer", broadcasting at full power from local sunrise to local sunset, and at reduced power from local sunset until 45 minutes later (during "critical hours"), after which it signs off to protect clear channel station WMVP in Chicago from skywave interference.
WIOO functions as a "daytimer", transmitting at full power from local sunrise until local sunset and at reduced power for 45 minutes thereafter (during "critical hours"). This practice aims to prevent interference with clear channel station WMVP in Chicago, which is vulnerable to skywave interference.