Trying to develop your aviation career is not an exact science. And trying to do it by numbers may mean you miss out on opportunities along the way.
Everyone will have different stories. My first flying job was flying PA31's & I had just over 400 hours total time when I started. Out of the 16,000 hours I now have, I only have 325 hours in total on singles. Sure, I missed out on some great flying on some great single-engined aircraft, but I did what was right for my family & I at the time. I have my regrets - everybody does.
So do what is right for you. When you feel it might be time to move on, then it probably is.