Thank you Daniel! Look For that we turn to this well-sourced article by John Major Jenkins, a student of Mayan time:
But how are we to relate this to a time frame we can understand? How does this Long Count relate to our Gregorian calendar? This problem of correlating Mayan time with "western" time has occupied Mayan scholars since the beginning. The standard question to answer became: what does 0.0.0.0.0 (the Long
Count "beginning" point) equal in the Gregorian calendar? When this question is answered, archeological inscriptions can be put into their proper historical context and the end date of the 13-baktun cycle can be calculated. After years of considering data from varied fields such as astronomy, ethnography, archeology and iconography, J. Eric S. Thompson determined that 0.0.0.0.0 correponded to the Julian date 584283, which equals August 11th, 3114 B.C. in our Gregorian calendar. This means that the end date of 18.104.22.168.0, some 5125 years later, is December 21st, 2012 A.D.1
Their End Date is as we thought 21st - 12 - 2012! But what time will we be offered the Extra Energy of Mind? The IMPETUS to sort things out for ourselves? When will we start to improve lives at all times in everyplace? Daniel can you startthe ball rolling by offering a reliable time?
Some little info: Mayan never had problems related to counting years for their cycles, because their main measurements of counting were based on astronomical events, solstices and equinoxes. So mayans might never worry about amount of days in years, they even had two calendaries - one is long counting based on solstices and equinoxes to have calculated 5125 years cycles, and civil calendar based just on amount of days in year - for farmer works etc. They even knew that second calendar is not perfect because year has ~365.26 that we know in modern times, but they never worry about that and civil calendar was slowly shifting over times - they knew that but not corrected, they just shifted dates of start of farmings etc, because they already had long count which satisfy they regarding all long scale events.
Problem with extra days appeared in Gregorian calendar of course because we would like to count years with fixed amount of days which is kind of wrong, so to have years matching earth cycles around sun we need to add +1 day every 4 years, and then +1 day on more long terms just to match our years with earth rotations around sun. Again mayans had no such problems because they counting days in "astronomical scale".
That's true that when mayan calendar was revealed nobody knew what is 0 date, but later by studying mayans documents about events in sky and comparing european sources they revealed some hints like appearing of comets in sky etc - well documented in both cultures. Those gave hints about matching two calendars. In these way two hypotheses were born about 21 dec 2012 and 22-23 dec 2012, but that's probably because of not perfect dates counting in western world times ago. Also scientists pointed that mayans would definitely prefer to bind end date (or next baktun) on astronomical event - winter soltice 21 dec 2012, or they whole calendar system is to be matching this day - this special alignment with sun.
So if you are looking about exact time you probably need to have binding to exact alignment for winter solstice 21 dec 2012, which is should be 11:12 UTC time - in the moment earth axis is perfectly aligned to be in same plane with sun.
Related all those discussions about rays from center of milky way, you should know that on the solstice sun is also will be in Sagittarius(18 Dec-18 Jan) where the center of galaxy is supposed to be (Sagittarius A*), so again earth will be aligned also to have kind of directed to galaxy center too. kind of
*(galaxy center) --------- * (sun) ---- / (earth axis)
Not sure about exact calculations regarding will it be really perfectly aligned to Sagittarius A* or not.