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. If you're working in a school that uses Google Apps for Education, your students can use their log-in credentials on YouTube so they don't have to create separate usernames and passwords.
The images below show you how to create a Photo Slideshow on YouTube. (Click the images to view them full size).
Step 1: Log into your YouTube account and click "upload" then click "Photo Slideshow."
Step 2: Select images from your Google Account or upload images from your computer.
Step 3: Drag and drop your images into the sequence in which you want them to appear.
Step 4: Choose a sound track and select the slide display duration and transition.
Step 5: Enter a title, description, and tags for your images. Select a thumbnail and privacy setting.
Step 6: Use the annotations tool to add text to each frame of your video. You can specify the length of time that each annotation is displayed for.
Watch my sample video below.