NSString

NSString *time = [[timeString stringByReplacingOccurrencesOfString:@"T" withString:@" "] substringToIndex:19];  

NSMutableString

 NSMutableString *string = [[NSMutableString alloc]initWithString:timeString] ;  
 NSRange range = NSMakeRange(0, [string length]);  
 [string replaceOccurrencesOfString:@"T" withString:@" " options:NSCaseInsensitiveSearch range:range]; 

NSMutableString 可修改字符串常用方法

应用实例

应用一

应用二

两种方法可以达到同一个效果显示时间