Is there any life hack for using calendar for events less than 15 minutes in the future?

Configuration
2

You can use the action homeassistant.reload_config_entry to reload the integration after adding the calendar event. This method probably isn’t feasible if you plan on calling it a lot… I don’t think events will be posted while the calendar is reloading, so it’s likely that the automations wouldn’t be reliable.

In my experience 2 minutes is the smallest reliable time span… 1.5 minutes sometimes works, but not reliably.

- action: calendar.create_event
  target:
    entity_id: calendar.example
  data:
    start_date_time: 
    end_date_time: 
- delay: 30  #This delay seems necessary in my experience, YMMV
- action: script.reload_calendar_automation
  data:
    calendars:
      - calendar.example
    automations:
      - automation.example

If you describe what you are actually trying to do (rather than how you are trying to do it) we may be able to provide better options.

Update 2025-09:

Instead of simply reloading the calendar it seems a little more reliable to use the following script:

Calendar & Automation Reload Script 
alias: Reload Calendar & Automation
fields:
  calendars:
    name: Calendars
    description: ""
    required: true
    selector:
      entity:
        multiple: true
        filter:
          domain: calendar
  automations:
    name: Automations
    description: ""
    required: true
    selector:
      entity:
        multiple: true
        filter:
          domain: automation
sequence:
  - action: homeassistant.update_entity
    metadata: {}
    data:
      entity_id: "{{ calendars + automations }}"
  - repeat:
      for_each: "{{ calendars}}"
      sequence:
        - action: homeassistant.reload_config_entry
          metadata: {}
          data: {}
          target:
            entity_id: "{{ repeat.item }}"
  - action: homeassistant.update_entity
    metadata: {}
    data:
      entity_id: "{{ calendars + automations }}"
description: ""
icon: mdi:calendar-question-outline

The script has open fields so that it can be used for any combination of calendar and/or automation, so the updated calendar event creation is as follows:

Create Calendar Event sequence 
- action: calendar.create_event
  target:
    entity_id: calendar.example
  data:
    start_date_time: 
    end_date_time: 
- delay: 30  #This delay seems necessary in my experience, YMMV
- action: script.reload_calendar_automation
    data:
      calendars:
        - calendar.home_assistant_events
      automations:
        - automation.notify_scheduled_reminders