Pathfinder 1E Magical Knack and class related Spell Like Abilities question

I'm trying to figure out how the Magical Knack trait interacts with class-granted spell like abilities.

For example, if I had a 1st level Summoner, I can use the Summon Monster I spell like ability to summon a monster for 1 minute.

If, at level 2, I took a level in Fighter, but I had the Magical Knack trait with Summoner as my chosen class, would my summoned monster last for 1 minute, or 2 minutes?

I'm trying to find the rules that make this clear and so far I'm coming up short.

Thanks in advance.