My airline was founded in September 2006, and I milked all the routes I could with A320 and ATR. When there were no more routes with demand, I opened a new hub in neighbour city in Jun 2007. Now most of the routes with demand are used up, and I have positive revenue, but I cannot open a new hub yet, it says "you have recently opened a new hub".
How long time does it take between hub openings? Is there a time limit, or is there other limits like number of routes/aircrafts,/revenue etc?