What was your dilution? How much did you overexpose the print? I've never used Arista Lith developer but I like the results that come out of 1+25 or weaker dilutions (more colour, less contrast). My exposures usually run in the 2-3 minute range, although I've done less and more. I like the colours in your prints (I currently like the muted look) but I agree with Mark that the blacks should be darker. One trick I've learned is to print a black border around the image -- usually the rebate, but sometimes I make one -- if it's not truly black, then the blacks in my print are probably not black enough either.
If it makes you feel any better, I've just finished trying out a new paper for lith with Fotospeed LD20 developer, and the development times ran from 22 minutes (the shortest) to over an hour. And that was in warmer-to-hot lith as well. After four hours I have 6 prints to show for it (and I was doing 2 at a time!). How many prints did you do? It's often worth doing a few (again, I usually do between 6-10 versions of the same image) to get different variations of blacks and colours. Depending on what you like, the first couple of prints can be either really great or really blah. Sometimes the prints keep getting better and better! It's hard to know when to stop. But take what I say with a grain of salt -- I'm far from being an expert, and this is just in my limited experience.