Why Did the Nazgul Wait at Crickhollow?

[Alcuin]

In Reader’s Companion, Hammond & Scull quote Tolkien’s notes on the attack on Crickhollow. These are archived at Marquette and are the source of the Unfinished Tales chapter “Hunt for the Ring”.

Khamûl led the Nazgûl operating inside the Shire. The Witch-king was at Andrath, the narrow defile through which the Greenway passed between the Barrow-downs and the South Downs, from whence he visited the Barrow-downs and stirred up the barrow-wights.

When Frodo and his companions crossed the Brandywine River, Khamûl set one Nazgûl to watch the Brandywine Bridge, and sent two eastwards along the Great Road to report back to the Witch-king. Khamûl and the other Nazgûl from Dol Guldur (“his companion”) entered Buckland by the North Gate.

…desiring to attract as little notice as possible he (mistakenly and against Sauron’s orders) sacrifices speed to stealth.

Khamûl and his companion search Buckland, but “they are at a loss,” since Buckland is not on the maps the Nazgûl took from Saruman’s spy. In the following citation from Reader’s Companion, p. 165, the material in square brackets appears in the text, since Hammond & Scull are in turn citing Tolkien’s notes.

On 28 September they find Crickhollow at night, but do not attack although [Khamûl] is aware that the Ring has been, or is still, there. [Khamûl] ?lurks near, and [his companion] is sent to bring [the rider by the Bridge] and the horses. Road between Bridge and Bree is thus left unwatched. [Early on 29 September Khamûl and the other two Riders] come back to Crickhollow and watch it as the night passes.

The Tale of Years in “Appendix B” of RotK has these entries for September:

28 The Hobbits captured by a Barrow-wight. Gandalf reaches Sarn Ford.
29 Frodo reaches Bree at night. Gandalf visits the Gaffer.
30 Crickhollow and the Inn at Bree are raided in the early hours. Frodo leaves Bree. Gandalf comes to Crickhollow, and reaches Bree at night.

Frodo left Crickhollow early on the morning of 26 September. On the same day, Khamûl gathered the other four Nazgûl who were with him. The Ring-bearer was already gone, but just gone; and it took Khamûl another two days to locate where he had been; then it took him another day to prepare an assault on the house. His orders were apparently to act as quickly as possible, but he “sacrifice[d] speed to stealth.” By doing this, Khamûl made an error at Crickhollow.