Just wondering if anyone could help me out with some code that I'm currently working on for uni. It's a sliding tile puzzle that I'm coding and I've implemented an A\* algorithm with a Manhattan distance heuristic. At the moment the time for it to solve the puzzle can range from a few hundered milliseconds to up to about 12 seconds for some configurations. What I was wanting to know is if this range in time is what I should be expecting? 

I've never really done any AI before and I'm having to learn this on the fly, so any help would be appreciated.