Six months to a year depending on the conditions. You want it to be nice and hot in the pile and not too dry (generally not a problem with manure). If there is a lot of straw mixed in with the manure, I think it takes longer. This is not based on anything "scientific" just my experiences.
I muck out stalls at the end of winter and put the manure in a pile. I use a little of it 6 months later in the late summer when planting my winter squash but the bulk isn't tilled in until the following winter for the spring garden.
If you want to get some use out of the manure while it's rotting, build a hot frame! I haven't done this yet, but I'm planning on building some this summer so I can use them next winter.
The more air that circulates through the compost, the faster it will break down. If you can rig up a system where the compost is turned regularly, like every couple of minutes, you could have it finished in a week. If you aren't up to building a device, turn the pile as often as you can.
__________________ Nothing is as strong as gentleness, nothing so gentle as real strength - St. Francis de Sales
It needs to be fully composted whcih means that when the pile is turned it will not heat up again. The pile needs to be over 145 degrees several times while composting to kill e.coli and other pathenogens. the outsides of the pile need to be turned in and allowed to heat up also.
When fully composted, the original raw material is unrecognizable--everything has decomposed into black,light textured compost.
130 degrees F, for three days-- turn, then repeat. Usually three turns will suffice for a "static" pile. If using windrows, the temp must be higher for a longer period of time, since windrows cool off faster. The first method will qualify a compost pile as "organic" as it actually destroys chemical residues that may be incorporated-- ie herbicides, fungicides, etc.
If worms can survive, the worms will remove chemical residue, as well, but the residue then stays in their tissues... sift out the worms, and one has less chemicals than one started with. vermiculture is SOOOO interesting.....
Living in the present is staying ahead of the past.