Hi there ConTroLx2,
It sounds to me like you have downloaded and have reached the usage limit of X-Plane 11 Demo Version, this version is purposely free and will run out of usage time within 15 minutes of gameplay to let you see if you like the game and it works on your computer. If you purchase X-Plane 11 Beta Full Version, you will be able to play and use the X-Plane 11 application as long as you want, and receive free updates for more Beta versions as well as when the full official game releases.
In short, yes, if you buy it, you'll be able to use it to your hearts contempt.
I hope I was able to help.