I do not have enough time to bake my bread. Can I refrigerate it or let it sit on the counter and bake it later in the day?
Yes, you can refrigerate bread dough, and in fact you will probably find that it will give you better, tastier results, because the yeast has more time to do its work. Any bread baker worth his salt (flour?) will tell you that a slow, cold rise is better than a fast, warm one.
You should refrigerate the dough immediately after mixing, not after a rise. Depending on the amount of yeast in your recipe, this can be for a few hours or even overnight. Allow the dough to warm up a little before baking.
Just to add to other answers, it's often easier to refrigerate for the first proof. That is: mix, refrigerate for a "first rise" (from a few hours to a few days), then remove from fridge, shape, and then let rise the second time until read to bake. (The second rise can take anywhere from an hour to a few hours, depending on amount and activity of yeast.)
It is possible to shape loaves before refrigeration, but it's more likely to produce an uneven rise or misshapen loaves. It can also be more difficult to judge when to bake, since the center of a large loaf will warm much more slowly after removed from the fridge. (If you shape after refrigeration, you can fold the dough a few times periodically to redistribute the heat and warm the loaf throughout more quickly.)
To answer the other part of the question about letting it "sit on the counter," that depends on your room temperature, how fast the dough rises, and other things. If you try this, you should generally be prepared to de-gas and shape the dough after the long rise, doing your final rise right before baking. (Otherwise, an overproofed dough could collapse during baking.) If you're just adding an extra hour or something to the rise time, this is unlikely to cause problems. If you need to let it sit on the counter for longer and the room is warm, you'll need to decrease the yeast content in the recipe.