Your input string does not match the format:
format: @"yyyy-MM-dd HH:mm:ss"
input: @"2013-7-25 5:16"
^^^ missing :00
You can fix it with a small code mod:
NSString *strSunRise = [NSString stringWithFormat:@"%d-%d-%d %d:%d:00", year, month, day, hour, minute];
^^^
(or by removing :ss
from the format string).