How long should tooltip be displayed?
Be concise
Tooltips should be as concise and clear as possible. Keep the text to 1 or 2 short sentences. If the information you need to communicate is longer than that, look into using a different design.
What makes a good tooltip?
An effective tooltip is interesting, relevant, valuable, and helpful. The main goal is to help users discover and learn something useful that they possibly wouldn't have gleaned by themselves. For the best results, make sure to segment your users to show relevant tooltips at the right time for the right users.
Should screen readers read tooltips?
The tooltip must be operable using both keyboard only and screen readers (with a reasonable interplay of default keys like Tab , Enter / Space , Esc , Arrow keys), as well as mobile screen readers: Simple tooltips should be displayed automatically.