With presenter cue, is it possible to change the size of the clock/ timer font? Also it is possible to use an image for the background of the timer clock?

With the current version it's not possible to change the font sizes and add a background image. We will most likely implement that in a future version. 
If you are interested in a custom version, please contact us either via PM or at support@nominari.com. 

Best
Jens