We can only get fairly large pellets (more like mini-cubes) here and I'd hate to see a horse try to eat those dry.
Our ratio to start with here is 1 part pellets to 2 parts water. Then play with it to find out what the horse likes. I would make mine the night before to be ready the next day any time. Minimum 12 hour soak for our mini-cubes. EVen in the summer where temps are in the 20 degree celcius range, 24 hour soaking did no harm.