I don't intend to hang about in this fest of ridiculousness. However...
I feel that it's necessary to explain that Zog is talking about time on an analogue or digital watch, keeping 12 or 24 hour time.
That is NEVER how Jews figure out when Shabbat is. (Yes, people who are knowledgeable have been saying this, and Zog doesn't get it. Understood.)
Still... The verses in question talk about evening.
Zog, it might be news to you, but it isn't the clock that we measure "when is Shabbat?", although it is rather useful. It is "when is 18 minutes before sundown." That changes from location to location, time zone to time zone, and whatever. That is for starters.
Second, some of the complications you have mentioned is what makes it difficult to travel before a holiday. But the thing is that Jews who observe Shabbat and our Biblical holidays (with the exception of Purim, and that is only because it was not mentioned outright in the Pentateuch) do not travel. So, wherever we are, we acknowledge sundown when we see it. The time on the clock is a mere convenience, because calculating the point when sundown is sufficient for Shabbat or a holiday to begin is tricky, if you aren't good at measuring time by the sun.
Any other method of "deciding when Shabbat is" based on 24-hour days is ridiculous, because that isn't a Jewish measure of time. Therefore, days in the summer are longer than days in the winter. It's not 24 hours.
Besides... Your "7 days from when you started" game ONLY works if you manage to be alone and you lost track of days. It means nothing for folks who are in civilization and can keep track of days and times.
Wherever you are, Friday is Friday, and when the sun sets, Shabbat begins. When it gets dark, or "you see three stars in the sky" on Saturday night, Shabbat ends. (It gets more complicated for latitudes above the Arctic Circle and below the Antarctic Circle, on the open sea, or in space, but the article that rosends cited explains things in far more detail.)
I refuse to waste more brainpower or energy on a fellow who is trying to tell me that Jews don't know what we are doing because he found a clever game with time that has nothing to do with Jewish law.