Visually Impaired Clock

I like this App for allowing students to monitor and manage time. It is high contrast which is good for visually impaired kids too! There is a negative background- black- with white numbers for the digital time. It displays only the hour and minutes. The bottom of the screen displays a red bar that begins at the left beginning at the top of the minute and then moves to the right as the minute comes to an end. I've had students set the iPad beside them as they work. When they know that they have 2 minutes for a task, they can monitor whether or not they are successful. A few times the iPad goes to sleep if the students have more than a few minutes to work. Not sure how to work around this. Anyone have any ideas?