You gain information about the future stability of the plane's traits. You know for certain whether the planar traits of the spell's area are going to change on their own within the next one minute per caster level, and which minute they will occur in (to the round, if within one round per caster level). You also learn if such a change will happen at all within one hour per caster level, and if it will happen at all in a wider time interval of unknown length. The DM rolls 1d10 secretly; on a 1, the interval is one month per caster level; on a two or three, one week per caster level, on a 4-7 one day per caster level, on an 8, 12 hours per caster level, on a nine it tells you nothing you didn't already know and on a 10 it gives a false positive.