Simple. Use MagLoft for free as long as you like!
The trial is unlimited which means you can use all of MagLoft for free until you are ready to publish and go live. You can create your content, preview your issues on your own devices and get the publishing information setup for as long as you need.
It's only when you want your magazine to go live in the app stores that you would have to activate your MagLoft subscription. We feel this is common sense ;)