If travelling from Kohima, you can get a direct state bus that leaves every afternoon at 1Pm and arrives in Mon the following morning at 7. Several private buses and taxis also leave around the same time everyday. From Mon, regular shared taxis take you to Longwa in upto 3 hours and charge around 200 Rupees per person.
If, however, you’re travelling from Guwahati, get off at the train station in Bhojo. From Bhojo, take a rikshaw to Sonari located only a few kilometres from Bhojo. From Sonari, regular shared taxis leave to Mon (for 300 Rupees). From Mon, another 3 hours in a shared taxi.
For Indians travelling to Nagaland, it is mandatory have an Inner Line Permit (or an ILP) to access its various districts. An ILP can be obtained in Delhi, Guwahati or in Dimapur.
There is no public transport in Nagaland on Sundays, given Sundays are a Church day.
The ideal time to visit Nagaland is between September and April. This is when the temprature is most pleasant. Just like the most of Northeast India, avoid visiting it during the time of the monsoon.