Times Ever. Each time this High Magic ability is chosen, it adds one additional formal caster level to another Ritual caster of the appropriate school (Earth or Celestial) in helping to assist in the casting of their Rituals. Note that this may be purchased even without purchasing any Formal Magic levels. No more than 10 levels of Formal Link can be used on any one Ritual Casting, no matter their source.
Bonus levels added through Formal Link are cumulative and last throughout the duration of the purchase.