about 15 minutes.

I just made a 20 by 20 square with a 2 pixel wide line ever 2 pixels, added a slight amount of ripple to it.

Then I took the square and cut it into an irregular shape and made it a smart object so I could rotate it all I wanted without loss.

When I layed down a roughly 100 by 100 pixel patch of these shapes I merged them and made them a new smart object then did the same thing with the group until I had covered a 1000 x 1000 canvas.

flattened that out. Put it in the top corner of a 2k by 2k canvas and laid out 3 more so that it was a 2 by 2 of the big patch.

Used the clone stamp tool to get rid of the seams and then cropped the canvas down to the center 1000 x 1000...poof repeating pattern.