The first time I used Calendar in June 2020, I set it to Central Time and AM/PM. There was some confusion on my group with the GIO event times not being what I thought I had entered. I chalked it up to user error. 

My second use of Calendar was yesterday. In the Timezone field I selected  "(UTC-04:00) Eastern Time (US and Canada) (EDT)". I changed the clock from AM/PM to 24 hours. 

I then created my event using the drop down menu for the times. I selected 1400 for the start and 1530 for the end. The Timezone field showed (UTC-04:00) Eastern Time (US and Canada) (EDT) as the default. 
I then pasted details in the description box. 
The message was delivered and it had this as the date and time: Tuesday, 22 September 2020, 3:30am to 2:00pm (UTC-04:00) America/NY. 
Somehow it transposed the start and end times as well as sending it with AM/PM. 

Given my earlier June experience I was extra cautious to make sure my start and end times were correct. I "know" I didn't confuse the start and end times when creating this event. 

So I went back in and edited it to "all day", which removed the incorrect times. I have the correct time listed in the calendar description so I figured if anyone referenced or subscribed, they would find the correct time in the description of my event. 

I subscribe to our groups GIO calendar on my iPad. The event description is full of added characters. For example in the Notes field of the event is: Tues Sep 22 ( x-apple-data-detectors://12 ) and ( tel:+1%20786%20635%201003 ) US -- 

Is this expected behavior?