does steam elongate bread cook time?
Creating steam at the beginning of the baking cycle has one goal: to keep the crust soft and pliable to allow for maximum oven spring.

Most breads are supposed to expand during the first phase in the oven. If the outer crust is already hard, it will prevent the expansion, either causing a dense interior or uncontrolled tearing of the crust - and in the worst case, both. Apart from steaming, slashing a loaf causes intentional weaknesses in the crust that allow expansion.

So how long should you steam?

Once the internal structure has started to solidify, the steam is no longer necessary. For my average two-pounds free-form loaf on a baking stone, I pour a generous cup of boiling water in at the beginning and then after about fifteen minutes I open the oven door wide to let the excess steam escape. Typically I also lower the oven temperature at this point.

For loaves in a pan, misting the loaf surface or adding a wash will also keep the crust pliable, similar to steaming.



But if I read your question correctly, I actually have another suspicion, why your bread stays cool inside or bakes longer:  

If you used wet cool towels, they will  


absorb a lot of energy from your oven and  
act as a kind of "shield" or "barrier" that unintentionally protects your bread from the oven's bottom heat.