Elsewhere in the New Advent Catholic Encyclopedia, the Ascension is indicated as the time. Under “Limbo”, it says:
“In theological usage the name is applied to (a) the temporary place or state of the souls of the just who, although purified from sin, were excluded from the beatific vision until Christ`s triumphant ascension into Heaven (the “limbus patrum”) …”
The limbus patrum = the Limbo of the Fathers.