Varible Calendar Trigger Offset

First off, I posted this in the wrong section earlier, so I do apologize for that.
Secondly, I could use some help lol. I’m new to all this, I’ve been able to follow a few basic tutorials for other things I wanted to do, but I haven’t had much luck finding info on this particular problem.

So what I want to do is be able to adjust the trigger offset from the frontend. This is for my wife, I have a calendar set up for when she works, but sometimes she needs to leave earlier than what the event is set for. Ideally I would have a drop down menu that would change the offset to HH:MM earlier than what the calendar even is set at.

Right now we are using google calendar to track what date and times that she works.

If there is a topic or topics that I have completely missed when searching, please point me in the right direction. I haven’t had any luck on figuring this one out on my own.

Thanks Y’all.

Not a solution, but another hand raised for dynamic offset, so in the end the improvement is about allowing templates in the offset.