I do recommend using an NSDate object to store the time the store closes instead of using your own custom integer format. It s unfortunate that NSDate represents both date and time of date.

In any case, you can check NSDateComponents. You can have a utilities method like:

int minutesSinceMidnight:(NSDate *)date
{
    NSCalendar *gregorian = [[NSCalendar alloc]
        initWithCalendarIdentifier:NSGregorianCalendar];
    unsigned unitFlags =  NSHourCalendarUnit | NSMinuteCalendarUnit;
    NSDateComponents *components = [gregorian components:unitFlags fromDate:date];

    return 60 * [components hour] + [components minute];    
}

Swift 5 This for exemple gives you the current number of minutes since midnight

let calendar = Calendar.current
let now = Date()

print(getMinutesSinceMidnight())

func getMinutesSinceMidnight() -> Int {
        return (calendar.component(.hour, from: now) * 60 + calendar.component(.minute, from: now))
 }

A swift version of what @notnoop has replied:

func minutesSinceMidnight(start : NSDate) -> Int {

    let units : NSCalendarUnit = [.Hour, .Minute]
    let components = NSCalendar.currentCalendar().components(units, fromDate: start)
    return 60 * components.hour + components.minute
}

If you have another NSDate which is set to midnight, then you can use the timeIntervalSinceDate method of the NSDate object to get an NSTimeInterval back with the difference between the two. Alternatively, if you re always wanting to compare midnight with the current time, you could call the timeIntervalSinceNow method on the midnight NSDate and you d get an NSTimeInterval back (albeit negative) with the difference between midnight and the current time.

NSTimeInterval is defined as a double by the standard which holds a number of seconds (and any fractional seconds).

This is a contemporary way without any extra math.

Objective-C

NSCalendar *calendar = [NSCalendar currentCalendar];
NSDate *midnight = [calendar startOfDayForDate:[NSDate date]];
NSInteger minutesSinceMidnight = [calendar components:NSCalendarUnitMinute fromDate:midnight toDate:[NSDate date] options:0].minute;

Swift 3+ as Date extension

extension Date {
    func minutesSinceMidnight() -> Int {
        let calendar = Calendar.current
        let midnight = calendar.startOfDay(for: self)
        return calendar.dateComponents([.minute], from: midnight, to: self).minute!
    }
}

Usage:

print(Date().minutesSinceMidnight())