Most disks will be dry to the touch within a minute, before this you can smudge if you slide you finger across with some pressure.
Also touching the surface of the disk within about an hour of printing (varies with disk surface type) will almost always leave a horrible greasy/fingerprint which will NEVER come out.
For disks you know are likely/going to be fequently handled you could try a fixative spray. A friend does and he can just wipe off marks with no problem, although at over Â£7 a can it not cheap, but is effective.
One more thing dont EVER be tempted to put a freshly printed disk straight into a drive of any kind. The rotational speed of the drive can cause any loose (wet/even almost dry) ink to run in "pretty" patterns to the edge of the disk due to centrifugal force. What this ink splatter does to the inside of the drive I dont know, but it surely cant be good (except perhaps in a decorative sense ).