Update
Timezone
I forgot to mention that the official campaign time is based on CEST timezone (Central European Summer Time). So, for example, when I say "midnight" it means "midnight in Italy", which would be eleven p.m. in England or 6 p.m. in New York.
This is important to know when you are going to create a game during the night between Sunday and Monday (to know if you are already into the next month with new planes available or not).