When is Navaratri celebrated?

Swamiji says:
Navaratri can be celebrated at any time. Most often it is observed from Pratipad to Navami or from Shashti to Purnima or Amavashya.

 

Are there six Navaratris?

Swamiji says:
There are four Navaratris which are special:  Magh, Chaitra, Ashadh, and Ashvin.  These correspond to winter, spring, summer, and fall.

 

Can you suggest any guidelines for people wishing to observe the Navaratri fast for 9 days, 24 hours with no water, no food?

Swamiji says:
Start off small and be content with small steps. Observe 24 hours with only water, then drink. Actually you will probably want salt more than water. Then try three days. And eat only fruits and water one time a day for the remainder of the nine days. Slowly you will extend it.

 

No grains, or salty food is to be eaten during Navaratri.  Are fruit and vegetables ok?  To fast with no food a greater tapas, and austerity.  Is this correct?

Swamiji says:
The fasting gives forth a number of benefits. We suggest that everyone observe the vow according to their own capacity: the needs of the body, the activities in which the body must engage during the vow, etc. Some will give up grains and pulses, some will only take fruit and dairy, some will only take water: each according to his or her own capacity.

 

How do we count Navaratri? Sundown to Sundown? Sunrise to Sunrise? Or Sunrise to Sundown?

Swamiji says:
We use a Panchanga, an almanac timed according to the phases of the moon.

 

Is it possible to do homa of 108 names of Durga Maa from the Chandi Path for Navaratri?

Swamiji says:
Yes.