Depends on the amount of heat available the amount of water you need to heat the amount of salt in the water and the heat transfer rate. I need more info
Many parasites and bacterium can be killed by boiling the water before consumption.
It depends on how hot it is. For example, if it is heated to 160o F, it will never boil.
ten minutes
Yes, at cold enough temperatures. You can watch this being done on many youtube videos during winter, with boiling water in fact. Around -30 or -40, boiling water will freeze before it hits the ground.
Distillation by boiling the water and then condensing the steam back into water will leave many contaminants behind.
50 minutes before noon.
The table on the website listed below shows many boiling points for many different elevations.
It could be instantly. In the far north of the world you can throw a cup of boiling water in the air and it will turn into ice before it hits the ground
20 minutes
15 min
Freezing = 0 Boiling = 100
It would be 40 minutes before 12.