A stretched spell has increased duration. The duration of the spell is increased by concentration. For example, sanctuary has a duration or 1 round/level; stretched sanctuary has a duration of Concentration + 1 round/level. If the duration of a spell is measured in rounds and does not scale with level, a stretched version of the spell takes up a spell slot one level higher than normal. Unlike other metamagic feats, applying stretch to a spell does not increase the amount of time required to cast the spell. Spells with durations of instantaneous or concentration can not be stretched.