TimeZones needs explaining to someone stupid

Embarrassing,
I have read numerous posts regarding timezone and my brain can't really understand it. Something is wired wrong in the central =)
My MT4 broker uses GMT+3 (icmarkets) and I live in GMT+1. So there is a 2 hour difference with my local time and with MetaTrader Chart.
However when summer its not GMT+1 but GMT+2? And then during winter back to GMT+1?

Where it gets confusing is when different markets closes and opens, and when using external data for processing that is created in a different zone.
Lets say I trade ET New York only....they open 8:00 AM and close 5:00 PM.
So by a simple brains math, as I have understood it there is a 7 hour difference between my MT4 charts time and ET time? Why? Because GMT+0 is 4 hours ahead of ET, but since broker uses GMT+3 its 7 hours difference and 5 hours difference with my local time.

When New York closes at 17:00, it means on my MT4 chart it is displayed as 24:00?
When New York opens it is 08:00 local time, but 15:00 at MT4 chart? Is this correct?

When New York opens it will show 13:00 on my local time will close 22:00 my local time?

Here is when it gets confusing for me. I sometimes pay for historical data on forex from a provider where the timezone is ET. Its a csv file starting from 00:00 to 24:00. So if I have understood it correctly data in this file from 08:00-17:00 is New York opening hours.

On a Friday when market closes at 23:59 in Metatrader and 22:00 my local time, it should logical mean that its the closing time of the New York session?
However the data from my CSV file on Friday continues to 23:59:00 - how is this possible if data comes from a provider EST?

Ok since it got all confusing I will write down main problem.
The data provider gives me a feed with timestamp 00:00:00 - 23:59:59. When asked what timezone the timestamp is in, they replied its Eastern Time Zone.

I live in Europe and market closes 24:00 on a Friday in MetaTrader, and that is 22:00 my local time. So far so good.
I get the feed in the morning of Sunday from the provider of the previous day forex sessions.

Last entry in this data is 23:59:59! How is this possible if its Eastern Time Zone?
Think my understanding and logic is corrupted =)

You not the only I also picked that up my MT4 is 1h ahead compare to my local time. The day I saw that I counted all the candles to the previous day and I found out that 23:00 candle was not formed.