Duration Per Level

When a spell lists duration as "plus X minutes per caster level," this refers to your current level, so adding from earlier level advancement applies.

Example: A 3rd level spell, Arcane Refuge you obtain at 3rd level states: "Duration: 15 minutes, plus 5 minutes per caster level." So at 3rd level it automatically protects you for 30 minutes (15 minutes + 3rd level).