|Is it to late in the year to till leaves into the garden?|
|No, early spring is a GOOD time to till the leaves into the garden. That's because they have now partially decomposed and are more readily broken down! Just be sure you don't till the garden when the soil is wet--wait until it has dried sufficiently so you are fluffing up the soil, not compacting it. And try to wait a few weeks after tilling the leaves in before you start planting.
You might want to add a bit of lime to help sweeten the soil.