Converting to Laravel Validator instead of doing the logic in the controller:

old.Controller.php

$start = $request->get('start');
        $end = $request->get('end');
        $project = $request->get('project_id');
        $task = $request->get('task_id');

        if ( ! $start || ! is_int($start))
        {
            return new Response(["error" => true, "message" => "Start time is not valid."], HTTP::BAD_REQUEST);
        }

        if ( ! $end || ! is_int($end))
        {
            return new Response(["error" => true, "message" => "End time is not valid."], HTTP::BAD_REQUEST);
        }

        if ($end < $start)
        {
            return new Response(["error" => true, "message" => "End time is before start time."], HTTP::BAD_REQUEST);
        }

        if ( ! $project )
        {
            return new Response(["error" => true, "message" => "Project not specified."], HTTP::BAD_REQUEST);
        }

        $project = Project::find($project);

        if ( ! $project )
        {
            return new Response(["error" => true, "message" => "Invalid project id specified."], HTTP::BAD_REQUEST);
        }

        if ( ! $project->status )
        {
            return new Response(["error" => true, "message" => "Project is not active."], HTTP::BAD_REQUEST);
        }

        if ( ! $task )
        {
            return new Response(["error" => true, "message" => "Task not provided."], HTTP::BAD_REQUEST);
        }

        $task = Task::find($task);

        if ( ! $task )
        {
            return new Response(["error" => true, "message" => "Task not found."], HTTP::BAD_REQUEST);
        }