The second ones appear after the Unbidden have 15% of the galaxy with a mtth of 12 months, the third ones appear with a mtth of 280 months after that.
Whoever you heard it from made it up. Jump Drives only affect the initial Unbidden invasion. Having one variant (regular or psi, they're treated equally) makes the trigger check more frequent (2000 years down to 200) and having both reduces it to 20. The end. The remaining two extradimensionals' arrival is conditional upon Unbidden expansion.If i remember correctly i read somewhere that the other extradimensional Factions appear earlier when there are more psi jump drives used in the galaxy...
so if in the whole galaxy just one empire has the tech and uses it only for a really small fleet, the other extradimensionals will need more time to arrive then in a galaxy where nearly everyone has psi jump drives and uses them excessive