I have found the answer to my problem with the method Martin has given from the post. This method converts an "Time" string like (18:00) to the date of today at 18:00.
Here it is:
- (NSDate *)todaysDateFromString:(NSString *)time
{
// Split hour/minute into separate strings:
NSArray *array = [time componentsSeparatedByString:@":"];
// Get year/month/day from today:
NSCalendar *cal = [NSCalendar currentCalendar];
NSDateComponents *comp = [cal components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit fromDate:[NSDate date]];
// Set hour/minute from the given input:
[comp setHour:[array[0] integerValue]];
[comp setMinute:[array[1] integerValue]];
return [cal dateFromComponents:comp];
}