For seed requiring warm stratification followed by cold stratification, I store the seed dry in the refrigerator until May, then soak 24 hours in water, then plant in the seed flat. Label the flat well with date planted and a "do not disturb for 2 years" note. Then leave the flat outside all summer, and winter with the appropriate hardiness group for the winter. A few may sprout right away, just let them grow. The bulk will sprout the following spring, and then there will be a few stragglers that will sprout the second spring. So plant in May 2015, main batch will sprout May 2016, and a few will come up 2017.
Maple seed if allowed to dry will follow this pattern, fresh maple seed, that ripens in spring (Acer rubrum & some others) will sprout right away, if planted immediately. But if a little dry will require the warm stratification followed by cold stratification. Fall ripening maples (palmatum & others) if kept moist and fresh, only need the cold stratification. But if any seed gets too dry needs they will sit dormant for the summer and sprout the following year.
Stewartia and many other species need the warm-cold treatment. This is why these species are so expensive. A pain to deal with.