How to use removeTimeRange method of AVMutableComposition?

Question

I have composed multiple videos and I want to remove last 0.5 second of all the tracks in the composition. I believe removeTimeRange can be used in situation. Doc for this methods reads as

Removes a specified timeRange from all tracks of the composition

But not able to figure out the range that should be given to achieve this. My composition code is following:

AVAsset *asset0 = [self currentAsset:0];
AVAsset *asset1 = [self currentAsset:1];
AVAsset *asset2 = [self currentAsset:2];
AVAsset *asset3 = [self currentAsset:3];
AVAsset *asset4 = [self currentAsset:4];

NSArray *assets = @[asset0, asset1, asset2, asset3, asset4];

AVMutableComposition *mutableComposition = [AVMutableComposition composition];
AVMutableCompositionTrack *videoCompositionTrack = [mutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo
                                                                                   preferredTrackID:kCMPersistentTrackID_Invalid];
AVMutableCompositionTrack *audioCompositionTrack = [mutableComposition addMutableTrackWithMediaType:AVMediaTypeAudio
                                                                                   preferredTrackID:kCMPersistentTrackID_Invalid];

NSMutableArray *instructions = [NSMutableArray new];
CGSize size = CGSizeZero;

CMTime time = kCMTimeZero;
for (AVAsset *asset in assets)
{
    AVAssetTrack *assetTrack = [asset tracksWithMediaType:AVMediaTypeVideo].firstObject;
    AVAssetTrack *audioAssetTrack = [asset tracksWithMediaType:AVMediaTypeAudio].firstObject;

    NSError *error;
    [videoCompositionTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, assetTrack.timeRange.duration)
                                   ofTrack:assetTrack
                                    atTime:time
                                     error:&error];
    if (error) {
        NSLog(@"Error - %@", error.debugDescription);
    }

    [audioCompositionTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, assetTrack.timeRange.duration)
                                   ofTrack:audioAssetTrack
                                    atTime:time
                                     error:&error];
    if (error) {
        NSLog(@"Error - %@", error.debugDescription);
    }

    AVMutableVideoCompositionInstruction *videoCompositionInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
    videoCompositionInstruction.timeRange = CMTimeRangeMake(time, assetTrack.timeRange.duration);
    videoCompositionInstruction.layerInstructions = @[[AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoCompositionTrack]];
    [instructions addObject:videoCompositionInstruction];

    time = CMTimeAdd(time, assetTrack.timeRange.duration);

    if (CGSizeEqualToSize(size, CGSizeZero)) {
        size = assetTrack.naturalSize;;
    }
}

AVMutableVideoComposition *mutableVideoComposition = [AVMutableVideoComposition videoComposition];
mutableVideoComposition.instructions = instructions;

mutableVideoComposition.frameDuration = CMTimeMake(1, 30);
mutableVideoComposition.renderSize = size;

pi = [AVPlayerItem playerItemWithAsset:mutableComposition];
pi.videoComposition = mutableVideoComposition;

player = [AVPlayer playerWithPlayerItem:[[CameraEngine engine] pi]];

player.volume = 0.75;
playerLayer = [AVPlayerLayer playerLayerWithPlayer: player];

playerLayer.frame = self.bounds;
[self.layer addSublayer: playerLayer];
[playerLayer setNeedsDisplay];
[player play];

I want to remove 0.5 sec of video from all 5 tracks after composition because I get blank frames in between when track changes.

All the tracks are fine(no black frame at the end). I have tried removing frames directly from AVMutableCompositionTrack but againg blank frames comes after composition.

So I want to know how to produce this time range?