How much time has passed...

[Young Vongola]

Between Nagato's death and the beginning of the war? Have they ever stated it?

 

[Seventh Sama]

a couple of months. probably

 

[Flawž]

This is interesting. Im sure it's not that long.

 

[Neonian]

almost 2 months

 

[TheSageOfNinetails]

Not exactly something that we can calculate accurately, but maybe if you really devote some time you can get a close estimate, but I would say at most 2-3 months.

 

[Huzaifa]

I don't really know try naruto wiki.

 

[Element Master]

almost 2 months

What this guy said