In order to answer this, you need to determine a standard definition of month, or you need to specify the specific months spanned. Months can be 28, 29, 30 or 31 days in duration.
21 days and no hours
1,350 hours = about 1.85 months (1.84808875 months)
8,000 hours = about 11 months (10.9516371 months)
12 months/year x 21 years = 252 months
250 hours = about 0.34 months.
21 days and no hours
5 months
The only desert that would have 21 hours of sunlight would be Antarctica during the summer months.
1,350 hours = about 1.85 months (1.84808875 months)
8,000 hours = about 11 months (10.9516371 months)
12 months/year x 21 years = 252 months
500 hours = 0.684477316 months
600 hours = 0.82 months.
855 hours is ~1.17046 months.
250 hours = about 0.34 months.
1065 hours = 1.46 months
480 hours is about 0.657098 months.