find_nearest_hour.yml

---
- hosts: localhost
  vars:
    hour_block_size: 4
  tasks:
    # To find the nearest hour within a X (hour_block_size) hour span (nearest neighbor), sort floor
    - set_fact:
        block_of_hours: "{{ ( ( ansible_date_time.hour | int ) // hour_block_size ) | int }}"
    - debug: msg="{{ [ ( block_of_hours | int ) ] | map('extract', range(0, 24, hour_block_size)) | list }}"