This card can only be activated during your opponent's Damage Step. During this turn, if you take Battle Damage of 2000 points or more, increase your Life Points by 4000 points before the damage is subtracted from your Life Points.
1/1/1970 is the start of what's known as "Epoch time" - which counts the number of seconds since that date. It's an easy way to store the current date/time and is simple to make readable.
Typically, when a website needs a placeholder for the date, like when it can't get the actual time, that date is used.
Check out epochconverter.com for more info or to see what the current epoch time is :)
2 things to take note of...
1. You can only activate when recieving 2000 or more damage from a single monster.
2. You cannot use multiple of this card at the same time.
Yeah, #1 is correct, but #2 isn't. During a duel, just tap the settings button at the top-right corner, scroll down, and tap the "Self Chain ON" option. Then, you can chain multiple cards at the same time. See: http://duellinks.gamea.co/c/yuu45q1k