NSDate的格式默认是的含有时分秒，关于NSDate通过Compare方法比较即可:

NSDate *currentDate=[NSDate date];
NSString *dateString = @"2016-05-04 16:59:00";
NSDateFormatter *formatter = [[NSDateFormatter alloc] init] ;
[formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

NSDate *mydate=[formatter dateFromString:dateString];
NSComparisonResult result=[currentDate compare:mydate];
switch (result) {
    case NSOrderedAscending: {
        NSLog(@"FlyElephant:%@--时间小于---%@",currentDate,mydate);
        break;
    }
    case NSOrderedSame: {
        NSLog(@"FlyElephant:%@--时间等于---%@",currentDate,mydate);
        break;
    }
    case NSOrderedDescending: {
        NSLog(@"FlyElephant:%@--时间大于---%@",currentDate,mydate);
        break;
    }
}

输出结果:
FlyElephant:2016-05-04 15:27:55 +0000--****时间大于****---2016-05-04 08:59:00 +0000

如果处理过时间，有可能会遇到，我们只是比较日期是相同，不需要比较小时分钟和秒数，除了将dateformate的格式修改为yyyy-MM-dd形式之后，我们还有NSDateComponents方式实现:

NSString *fromDateStr= @"2016-05-05 06:00:00";
NSString *toDateStr= @"2016-05-05 8:59:00";
NSDateFormatter *formatter = [[NSDateFormatter alloc] init] ;
[formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
NSDate *fromDate=[formatter dateFromString:fromDateStr];
NSDate *toDate=[formatter dateFromString:toDateStr];
if([fromDate isEqualTo:toDate]){
    NSLog(@"FlyElephant:%@---等于---%@",fromDate,toDate);
}

toDate=[[NSDate date] dateByAddingTimeInterval:60*60*100];
if([fromDate isEarlierThan:toDate]){
    NSLog(@"FlyElephant:%@---小于---%@",fromDate,toDate);
}
toDate=[fromDate dateByAddingTimeInterval:60*60];
if ([fromDate isEarlierOrEqual:toDate]) {
    NSLog(@"FlyElephant:%@---小于等于---%@",fromDate,toDate);
}

toDate=[[NSDate date] dateByAddingTimeInterval:-60*60*100];
if([fromDate isLaterThan:toDate]){
    NSLog(@"FlyElephant:%@---大于---%@",fromDate,toDate);
}

toDate=[fromDate dateByAddingTimeInterval:-60*60];
if ([fromDate isLaterThanOrEqual:toDate]) {
    NSLog(@"FlyElephant:%@---大于等于---%@",fromDate,toDate);
}

时间比较结果:
<pre>
**2016-05-04 23:38:44.754 FECategory[31727:405193] FlyElephant:2016-05-04 22:00:00 +0000---****等于****---2016-05-05 00:59:00 +0000** **2016-05-04 23:38:44.754 FECategory[31727:405193] FlyElephant:2016-05-04 22:00:00 +0000---****小于****---2016-05-08 19:38:44 +0000** **2016-05-04 23:38:44.755 FECategory[31727:405193] FlyElephant:2016-05-04 22:00:00 +0000---****小于等于****---2016-05-04 23:00:00 +0000** **2016-05-04 23:38:44.755 FECategory[31727:405193] FlyElephant:2016-05-04 22:00:00 +0000---****大于****---2016-04-30 11:38:44 +0000** **2016-05-04 23:38:44.756 FECategory[31727:405193] FlyElephant:2016-05-04 22:00:00 +0000---****大于等于****---2016-05-04 21:00:00 +0000**
</pre>

时间分类实现:
<pre>`
//
// NSDate+FEDateCompare.m
// FELabel
//
// Created by FlyElephant on 16/5/4.
// Copyright © 2016年 FlyElephant. All rights reserved.
//

import "NSDate+FEDateCompare.h"

@implementation NSDate (FEDateCompare)

-(NSComparisonResult)compareDateByDay:(NSDate *)date{

NSDate *fromDate=[self formatDateByComponent:self];
NSDate *toDate=[self formatDateByComponent:date];

NSComparisonResult result=[fromDate compare:toDate];
switch (result) {
    case NSOrderedAscending: {
        return NSOrderedAscending;
        break;
    }
    case NSOrderedSame: {
        return NSOrderedSame;
        break;
    }
    case NSOrderedDescending: {
        return NSOrderedDescending;
        break;
    }
}

}

-(BOOL)isLaterThanOrEqual:(NSDate *)date{
NSDate *fromDate=[self formatDateByComponent:self];
NSDate *toDate=[self formatDateByComponent:date];
return !([fromDate compare:toDate]==NSOrderedAscending);
}

-(BOOL)isLaterThan:(NSDate *)date{
NSDate *fromDate=[self formatDateByComponent:self];
NSDate *toDate=[self formatDateByComponent:date];
return ([fromDate compare:toDate]==NSOrderedDescending);
}

-(BOOL)isEarlierOrEqual:(NSDate *)date{
NSDate *fromDate=[self formatDateByComponent:self];
NSDate *toDate=[self formatDateByComponent:date];
return !([fromDate compare:toDate]==NSOrderedDescending);
}

-(BOOL)isEarlierThan:(NSDate *)date{
NSDate *fromDate=[self formatDateByComponent:self];
NSDate *toDate=[self formatDateByComponent:date];
return ([fromDate compare:toDate]==NSOrderedAscending);
}

-(BOOL)isEqualTo:(NSDate *)date{
NSDate *fromDate=[self formatDateByComponent:self];
NSDate *toDate=[self formatDateByComponent:date];
return ([fromDate compare:toDate]==NSOrderedSame);
}

pragma mark - private

-(NSDate *)formatDateByComponent:(NSDate *)date{
NSCalendar *cal = [NSCalendar currentCalendar];
NSDateComponents *components = [cal components:(NSCalendarUnitEra | NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay) fromDate:date];
return [cal dateFromComponents:components];
}

@end
`</pre>