[The Might]

As he stared out into the gloom, a black shadow moved under the trees; the gate seemed to open of its own accord and close again without a sound. Terror seized him. He shrank back, and for a moment he stood trembling in the hall. Then he shut and locked the door.

The night deepened. There came the soft sound of horses led with stealth along the lane. Outside the gate they stopped, and three black figures entered, like shades of night creeping across the ground. One went to the door, one to the corner of the house on either side; and there they stood, still as the shadows of stones, while night went slowly on. The house and the quiet trees seemed to be waiting breathlessly.
There was a faint stir in the leaves, and a cock crowed far away. The cold hour before dawn was passing. The figure by the door moved. In the dark without moon or stars a drawn blade gleamed, as if a chill light had been unsheathed. There was a blow, soft but heavy, and the door shuddered.

Fatty Bolger had not been idle. As soon as he saw the dark shapes creep from the garden, he knew that he must run for it, or perish. And run he did, out of the back door, through the garden, and over the fields. When he reached the nearest house, more than a mile away, he collapsed on the doorstep. "No, no no!" he was crying "no, not me! I haven't got it!"

Ok, so I guess that the "while night went slowly on" part suggests they waited. I disagree.
Just a quick timeline:

• Fatty Bolger sees something move outside and the gate open
• The three shadows open the gate and enter and surround the house
• Fatty immediately makes a run for it and calls for help

Now I don't know how quickly a hobbit runs a mile, but this is the time that passed from the moment the shadows entered to the moment the alarm was raised. Considering how afraid Fatty was I expect he ran that mile pretty fast.