Job Create Failed: 1 hour vs 1 hours

Hello. When I deploying, I failed creating my job. And my error log is here.

06:34:25PM CREATE_FAILED AWS::CloudFormation::Stack TemperatureJob Embedded stack arn:aws:cloudformation:ap-northeast-1:708995463862:stack/pongdang-prod-TemperatureJob-O7NBPVK79FKX/8e709410-8519-11e9-84d1-0a37482a4654 was not successfully created: The following resource(s) failed to create: [FooooEventsRule, FooooPermission].

And after I tried to many time, I can assume two reasons why creating job is failed.

First of all, TemperatureJob seems to be reserved. but my job name was TemperatureJob. So creating is failed.
Second of all, I can read below detailed log from AWS CloudFormation.

Parameter ScheduleExpression is not valid. (Service: AmazonCloudWatchEvents; Status Code: 400; Error Code: ValidationException; Request ID: 97940eaa-8519-11e9-b5a3-9b9aceff862f)

And my job code is here.

class MigJob < ApplicationJob
  class_timeout 300 # 300s or 5m, current Lambda max is 15m

  rate '1 hours' # every 10 hours
  def dig
    puts 'done digging'

So I assume rate '1 hours' maked error. and I change 1 hours into 3 hours, then creating is success.
If my assumption is correct, then docs should be updated, and please tell me why rate 1 hours makes error.

I found, when I change rate '1 hours' into rate '1 hour' then creating job is success.