Trigger on TIME Helper +/- N minutes for wake-up alarm

Hi, i currently have an automation with a fixed time (trigger AT 7.30) which start doing some automations for the wake-up routine. Indeed the trigger are 3, at 7.30 7-45 8.00 for dimmer the opening of the blinds.

The optimal would be to set an object Helper - Time and use this as trigger. It’s simple for a one-shot routine, but it’s impossible to add the conseguential trigger (TriggerHelper + 15 minutes and TriggerHlper + 30 minutes).
There’s a template for XX minutes before/after sunrise but not for a time helper.
I can workaround by creating two other time helper and a specific automation for change the respective time according to the principal helper, but it’s far from a clear solution.

Any idea for a template?