RNG'd for Latios today, I was not expecting for it to be easy... yet I got him in just one afternoon?
Here's what basically go does down with Latios/Latias, the frame advances it takes are very dependent on what seed you use, so you'll have to do some calibrating. So I'll make a quick guide to ease the job for others.
1) Advance your estimated frames using Radio/128 Steps, no one moves inside the Pokemon Fan Club so it's safe to do so.
2) Leave the fan club and talk to steven, he'll tell you aboot Lati@s and leave, after leaving the fan club and talking to steven the most common number of frame advances is 9, so use that as your initial trial.
3) Head to Mt. Silver (or any other place with high leveled pokemon) and catch a pokemon for you to check if you landed your seed/delay and the pokemon's ivs. If it doesn't match, repeat steps 1-3 till you do. (Wild Pokes are Method K, remember that) Determine the wild pokemon's frame position in method K
4) Find your Lati, this gets annoying, but I recommend traversing between route 13, 14 and 15. Make sure you catch them to see if you got them (use Method 1, obviously)
5) If you didn't get your target lati don't fret, check it's IVs and find what frame you hit. In order to determine the amount of frame advances follow this formula:
(Wild Pokemon Frame - Lati frame [Not desired, the one you got] - number of advances)
That should point to the amount of frame advances for said seed for the event from Leaving the fan club to the end of the steven conversation. Add or subtract the necessary numbers of advances and repeats step 1-4. 5 again if you need to
My trials:
So I aimed for seed FC0C01F7, Timid, 23/31/31/30/27/30, HP Fire 70, Frame 16. I initially went with 7 as my initial number of adavances but it didn't work after running down the formula listed in step 5, I found out the Lati frame was 7 for this seed. So I went with 9 advances and I smiled when I finally got my desired Latios.
Feel free to use the seed I used, it makes it SOOOOOO much less painful to RNG.
Successful test was successful!