Not only must you be up and out by dawn.

They were up at first light, and on the road by dawn.

You should be back by dawn or a little after.

It took hours before anyone was certain, but by dawn all could tell.

By dawn they were already a long way from the sea and turned back to look.

I'll have a word with the Chief, and we'll be under way by dawn.

By dawn the next morning they had covered some five miles to the south.

They were safe, and should be able to make it by dawn.

By dawn, she did not need to correct me any longer.

We had to have the pile in place by dawn.