I have a simple less files with very little contents but the compile time varies from 10 - 27s. Any ideas as to why? Is it my machine or the grunt settings that I am missing? Do I need to clear some sort of cache?
Gruntfile.js contents
module.exports = function(grunt) {
  // Project configuration.
  grunt.initConfig({
    pkg: grunt.file.readJSON('package.json'),
    less: {
      development: {
        options: {
          paths: ["../css"]
        },
        files: {
          "../css/main.css": "../less/main.less",
        }
      },
      bootstrapBuild : {
        options : {
          paths: ['../css']
        },
        files : {
          "../css/bootstrap.css": "../less/bootstrap.less",          
        }
      }
    },
    watch: {
      options: {
        livereload: true
      },
      markup: {
            files: ['../*.php', '../inc/*.php'],
            options: {
                livereload: true,
            }
      },
      scripts: {
        files: ['../js/*.js'],
        tasks: [],
        options: {
          livereload: true,
          spawn: false
        },
      }, 
      mainCSS: {
        options: {
          livereload: false,
          spawn: false
        },
        files: ['../less/main.less', '../less/responsive/*.less', "../less/common.less"],
        tasks: ['less:development']
      }, 
      bootstrapBuild : {
        options: {
          livereload: false,
          spawn: false
        },
        files: ['../less/*.less', '!../less/main.less', "!../less/common.less"],
        tasks: ['less:bootstrapBuild'],
        spawn: false
      }, 
      css: {
          files: ['../css/*.css'],
          tasks: []
      }   
    }
  });
  // Less
  grunt.loadNpmTasks('grunt-contrib-less');
  // Watch
  grunt.loadNpmTasks('grunt-contrib-watch');
};
Package.json contents
{
  "name": "Project-Markup",
  "version": "0.1.0",
  "devDependencies": {
    "grunt": "^0.4.5",
    "grunt-contrib-nodeunit": "^0.4.1",
    "grunt-contrib-watch": "^0.6.1",
    "grunt-contrib-less": "^0.11.4"
  }
}
main.less contents
body{
    background: red;
}
/* End of Main */