// double -> NSNumber
NSNumber *doubleTime = [NSNumber numberWithDouble:123.123123123];
// NSNumber -> NSTimerInterval = double
NSTimeInterval *timInterval = [doubleTime doubleValue];
// double -> NSNumber
NSNumber *doubleTime = [NSNumber numberWithDouble:123.123123123];
// NSNumber -> NSTimerInterval = double
NSTimeInterval *timInterval = [doubleTime doubleValue];