When disney brought back only 16 districts, they forgot about the invasions and such.
What happens is with invasions, why they are so short now is because there are so many people on the districts, so the server only makes the invasion about 0-20 mins now. The server makes the invasions by how many toon are on the district.
My invasion stats
(From long countless hours searching for invasions)
0-30 toons: 1-3 hours
30-100 toons: 0-1 hour
100+ toons: 0-30 mins
If you want, you can complain to disney through this
link about the invasions, and whatnot.
I hope this helps.