You can use 24 but a short break is recommended. I use 20/4 with excellent results and others use 18 but some time off from the light is best for the plant. Moving them in and out is ok but watch for leaf burn from the sun. If they're not used to direct sunlight they can quickly burn their leaves. I start my indoor plants that have moved outside under trees so they can gradually be intoduced to the sun over a week or so by moving it from the shade a little more each day.