Spirit Timer Cap?

What is the current smallest reduction in time for spirits casting spells?

I have seen the equation:
48 - ((Summoner Skill - Skill Cap)/3) - Day/Weather/Astral Flow bonus

I have not been able to find any refrence to a cap to the amount of time reduction. I have also seen SMN's forum signature saying "529 Summonining Skill". If that is true the timer looks like

48 - ((529 - 417)/3) = ~10 Seconds
< ~5 Seconds with correct day/weather

Has anyone experienced a Spirit Timer Cap or does the spirit really cast spell, 5 seconds, cast spell, 5 seconds, etc...