Start the game on Fredas
Morrowind, unlike the other TES games, doesn't include days of the week. The Lua API gives us the ability to format dates including the name of the day. Currently the starting day appears to be an arbitrarily chosen Monday - presumably because it is the first day of the week in various places. If we however look at Daggerfall and Oblivion, we can conclude that Morrowind should start on a Friday.
The calendar implemented in OpenMW, Oblivion, and MCP-patched Morrowind.exe is much like the Gregorian calendar. Unlike the real life calendar, it doesn't implement leap years or months that vary in length from year to year, leading to a consistent 365 day year. Note that Daggerfall does not implement this calendar. It has 30 day months per the UESP.
Oblivion starts on Monday 3E433-08-27. Morrowind starts on 3E427-08-16, 2201 days earlier. Daggerfall starts on Thursday 3E405-01-04, 8254 days before Morrowind using the latter's calendar.
2201 % 7 = 3
and 8254 % 7 = 1
. Monday - 3 is Friday and Thursday + 1 is likewise Friday.
Skyrim is out of scope due to being in the 4th era, but we can conclude that the 4th era started about 3.5 years after Oblivion started if we want to align its Sunday with this calendar.