Maybe 15 minutes each, some less...it really depends on the colors and shapes of what I'm drawing. The frog thumbnails for example took closer to 15-20 minutes, whereas something like the panda would take me closer to 5 min. I charge $20/hr for all the art/web work I do anyway, so that's where 5 for $25 comes from.
How long did it take you to do that egg?!