Looking at buying a stave online, they were cut in April to August this year.

Bark is off ends and back have been sealed.

Advice ???

Depending on the dimensions of e stave, it'll probably take a year or more to dry.

If you reduce the stave to near bow dimensions it will dry much faster.

It 68.5 long 2/12 wide 3 thick

At those dimensions, a good 2 years. Rough it down closer to a bow dimension and you are looking at 1 year at the very least. The longer Osage dries, the better bow it will make. There are guys who dry Osage for 5 years to attain a premium stave. I won't even begin to make an Osage bow till at least two years of drying right after cutting down the tree. Three is better, four is sweet, and 5 is perfect.

I went ahead and got it, it was cut March of this year.

That is fine Adam. Depending on what weight bow you are looking for, it's possible to cut that stave in half width and thickness wise and get 4 bows out of it. Or at the very least cut it in half thickness wise and get 2 bows. It's better to go for 2 bows than push it for 4 bows. Or depending on how nice the stave is, just cut it down closer to a rough bow shape and then let it dry for at least 6 months, then make one bow. But the longer it dries, the better bow it will make.