You can change that by editing the mask_main.bmp, the part you want to change is the brown mask top right like in the image below.
Remember to move the pixels up top as well. The total time display by itself isn't a normal skinning feature in XMPlay, so it was put in using a trick to hide the other elements. Unfortunately it means that making it wider for 10+ minute times will push it out of alignment when its less than 10 minutes or will cut off again if more than 60.
It'll probably added as a real skinning feature at some point there's no perfect solution for it right now, if you want you could just remove the brown mask entirely and save yourself the hassle.