How to make the bottom of breads bake a little slower so that the whole bread could stay longer in the oven?
First, you can bake the bread on a higher rack. 

Second, you can turn up the temperature of the top heating element. 

Third, you can use a less heat conductive pan. 

Fourth, you can use a wash on the bread which turns brown quicker than normal dough. Egg yolk browns very nicely. On lean breads, a milk wash also does well. 

The way you describe it, you indeed have to address the issue. But be careful not to overdo it. To get well risen bread, you want to have higher temperature on the bottom than on the top, so the upper crust won't set too early. You will have to test your way changing the conditions towards the optimum.