Initial Z Negative Triangle

I want to make an initial triangle in the Z negative hemisphere of my world so that I can add triangles on around to the 'front' of my world...
I need a seed, in this case derived from milliseconds since time began in 1970, or at least as far as Javascript is concerned.
(I will want to add an input to get seeds from the user)

Seed: 1744724084321 ms since first internet millisecond! 8-P
This gives me a repeatable version of JS' random # 0.4459124095393463
x0: 418, y0: 455, z0: 195
x1: 339, y1: 293, z1: 14
x2: 290, y2: 440, z2: 75
polygon(418px 455px, 339px 293px, 290px 440px)
Cross Product is cx: 16725, cy: 13688, cz: -19551, triangle area: 14571 px^2