Hallo, i've a question. in sura 2:187 the duration of fasting is clearly maintained. No maintaining about it's limit of application. So if someone live in a place where sun never goes down for months and never rise for months, can people apply the hadith below?

Hadith - Muslim #7015, Narrated An-Nawwas ibn Sam'an
Allah's Apostle mentioned of the Dajjal one day in the morning. He sometimes described him as insignificant and sometimes described (his turmoil) as very significant (and we felt) as if he were in the cluster of the date-palm trees. When we went to him (to the Holy Prophet) in the evening and he read (the signs of fear) on our faces, he said: What is the matter with you?
We said: Allah's Apostle you mentioned the Dajjal this morning (sometimes describing him) as insignificant and sometimes very important, until we began to think he was present in some (nearly) part of the cluster of the date-palm trees.
So he said: I harbour fear in regard to you in so many other things besides the Dajjal. If he comes forth while I am among you, I shall contend with him on your behalf, but if he comes forth while I am not among you, a man must contend on his own behalf and Allah will take care of every Muslim on my behalf (and safeguard him against his evil). He (the Dajjal) will be a young man with twisted, cropped hair, and a blind eye. I compare him with AbdulUzza ibn Qatan. He who among you will survive to see him should recite over him the opening verses of Surah al-Kahf (xviii). He will appear on the way between Syria and Iraq and will spread mischief right and left. O servant of Allah! Adhere (to the path of Truth).
We said: Allah's Apostle , how long will he stay on Earth?
He said: For forty days, one day like a year, one day like a month, one day like a week, and the rest of the days will be like your days.
We said: Allah's Apostle will one day's prayer suffice for the prayers of the day equal to one year?
Thereupon he said: No, but you must make an estimate of the time (and then observe prayer).

(can anyone tell me about the authenticity of this Hadith)

How can people start the month fasting in space where moon always can be seen. And add the above question here also.