If I recall from my youth, that being the only firewood cutting I ever did, for the easiest splitting you need to split them within a day of so of cuttting them or wait till they dry completely like about a year later. Green they split good, dry they split good, but wait a week or two and they wont split easily at all at least not with a maul as it just bounces out. If you have a hydraulic splitter I suppose you could do it whenever you wanted but it would work the splitter harder.
The same goes for burning when clearing forest. You can burn green trees if you let them set for only 3-4 days till the leaves start to dry out and they will burn completely. If you let them set for a week or two, they will only smolder and only the small stuff with burn. When the wood starts smelling soured it wont burn very well. You have to burn within a few days or let them set for about a year to dry out completely.