How long is too long for sous vide steak
When cooking low temperature, over time the texture of the protein that you are cooking changes.  For a tough cut, like a shank, or short rib, this is desirable, and where you would see cooking times of 12, 24, 48 hours...or longer.  Most people want to enjoy a steak that chews like the traditionally cooked product.  After 3 to 4 hours, the texture of your steak will change.  It will become more mushy.  That is why it is recommended that you only cook until done (1 to 2 hours).  So, overdoing it, as you describe it, would be cooking it too long so that the texture becomes undesirable. For a steak, I think 4 hours would be pushing it.