How much in advance of planting vegetables should you fertilize a garden with chicken manure?
I would recommend doing a soil test on the soil prior to planting and fertilizing.
This will take the guess work out of what your soil may need.
You local County Extension Office can help you with a soil test.
Here is a link to find your closest office.
Fresh chicken manure should not be used directly on a garden bed. It should be properly composted, which can take 6 to 9 months.
Here is a link with more information.