YouTube Photo Slideshows don't have a time limit other than the standard 15 minute limit applied to all new YouTube accounts (there are work-arounds for this).
YouTube Photo Slideshows allow you to specify the length of time that each image is displayed for. After uploading your images you can use the annotations tool to add as much text as you like to each frame of your video.
Via Baiba Svenca
This is a great guide
If you have a YouTube channel, you might want to check this out!
good ...!