Wow - the day before sounds rather extreme! I'm not sure I'd do that if I were you, but I guess it might pay off - I switched to visual about 10 months ago and cut a couple of minutes off of my time almost immediately, so it might work.
For me, the biggest advantage of visual is repetition - you can go over a visual memorization of all 12 EP pieces in probably less than 2 seconds, so you can go over it 10 times in less than 20 seconds. So just repeat it again and again, and the whole thing will stick in your head. Still, patterns are helpful, and it can be useful to break it up in groups to remember it easily.
Let's take the really easy lucky scramble Rowe posted earlier today. It had no CP (amazing! how did that happen??), but a decent EP that you can work with. Scramble:
R' F2 R2 U' D B' L' F D R' L' B2 F U' D L2 D' B2 R2 F L' R2 D' L' R'
I always start from the front right, numbering like Macky does: 1 is UF, 2 is UL, 3 is UB, 4 is UR, 5 is LF, 6 is LB, 7 is RB, 8 is RF, 9 is DF, 10 is DL, 11 is DB, 12 is DR. So this scramble gives you cycles (1 12 11 4 10 6 9 2 3) (5 7 8) (assuming you scramble in the orientation you solve, which I actually didn't do when I tried this, but for this example we'll go with this). The first 4 in the first cycle (1 12 11 4) are easy to remember because they're up, down, down, up, with the downs shifted 90 degrees around the cube from the ups. I imagine a rubber band going between those 4. Then I'd notice the 10 is directly opposite the 4, and that the 6 and 2 go up the left side, with the 9 in between the 6 and the 2, and then the last one, the 3, is following the same line as the 10, 6, and 2. So really I see a line between the 10 6 2 and 3, and then mentally "insert" the 9. The last 3 are easy - they're all in position for a M' U2 M U2 algorithm to fix them if you rotate the cube z'. So I actually remember that to picture them.
I don't know that this actually helps you any, but at least it's an example. Really, it is true that the shapes just start to imprint in your mind after doing them a while; it's hard to talk through it to help you much. If you're planning on using this method tomorrow, my biggest suggestion would be to make sure you repeat the memorization over and over tracing it with your finger until you're sure you've got it. It looks like at your first competition you got all DNFs, so you should be able to beat that pretty easily by taking an extra 30 seconds or so to repeatedly retrace your EP. If I want a safe solve, I always memorize the EP, memorize the CP, then retrace all of the EP and all of the CP, and I won't go on to orientation until I can get all of the permutation right first.
Good luck - I hope you have success!
Edit: One other thing I do that I think helps is that I count the pieces as I go. So for the example above, I would point to 1 and say "1", then to 12 and say "2", then to 11 and say "3", then to 4 and say "4", then to 10 and say "5", then to 6 and say "6", then to 9 and say "7", then to 2 and say "8", then to 3 and say "9". Then I'd pause, then point to 5 and say "10", to 7 and say "11", and to 8 and say "12". That seems to give me an extra thing to hang my memorization on, so it helps in recalling, and it doesn't really slow you down at all. I don't think about the numbers I'm counting; I just mentally "say" them, and it seems to help. It helps me, at least.
