WFM Schedule Import 400 Bad Request via Platform API

Quick question about the WFM schedule import endpoint. Our Premium AppFoundry integration is hitting a validation error when posting agent assignments for the upcoming week.

{
 "errors": [
 {
 "code": "WFM_SCHEDULE_INVALID",
 "message": "Invalid time range for agent assignment."
 }
 ]
}

The payloads pass local validation checks, yet the API rejects them immediately. Is there a specific timezone offset requirement for the start/end timestamps in the api/v2/wfm/schedules payload?