As title, is there an estabilished time to pass to reenter a System after retreated from that?
If:
- there are no other targets in expansion range that have not previously been retreated from, or those that are would require an invasion
- and this is the closest of the previously-retreated non-invasion systems to the expansion source
- and the tick is processed for the retreating system before the expanding system
...then it can happen immediately and you might not even notice they were gone.
This is so far as I know the only time that's actually happened
(Lobos de Loki retreat then immediately re-expand to the system they just 'left')
...examples with a 1 or 2 day absence are much more common.
If on the other hand the retreat occurs early in a faction's existence and they have plenty of other eligible non-invasion targets, it might take them years to return.