利用时间戳来准确计算某个时间点具现在的时间差，可以参考 CocoaChina 会员 “” 分享的下面这段代码

- (NSString *)intervalSinceNow: (NSString *) theDate
{

NSDateFormatter *date=[[NSDateFormatter alloc] init];
[date setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
NSDate *d=[date dateFromString:theDate];

NSTimeInterval late=[d timeIntervalSince1970]*1;


NSDate* dat = [NSDate dateWithTimeIntervalSinceNow:0];
NSTimeInterval now=[dat timeIntervalSince1970]*1;
NSString *timeString=@"";

NSTimeInterval cha=now-late;

if (cha/3600<1) {
timeString = [NSString stringWithFormat:@"%f", cha/60];
timeString = [timeString substringToIndex:timeString.length-7];
timeString=[NSString stringWithFormat:@"%@分钟前", timeString];

}
if (cha/3600>1&&cha/86400<1) {
timeString = [NSString stringWithFormat:@"%f", cha/3600];
timeString = [timeString substringToIndex:timeString.length-7];
timeString=[NSString stringWithFormat:@"%@小时前",天龙八部私服, timeString];
}
if (cha/86400>1)
{
timeString = [NSString stringWithFormat:@"%f",劲舞团私服, cha/86400];
timeString = [timeString substringToIndex:timeString.length-7];
timeString=[NSString stringWithFormat:@"%@天前", timeString];

}
[date release];
return timeString;
}