Heed no nightly noises

[ainur]

In UT "The Hunt for the Ring" it says

the Black Captain established a camp at Andrath, where the Greenway passed in a defile between the Barrow-downs and the South Downs . . .While he himself visited the Barrow-downs. In notes on the movements of the Black Riders at that time it is said that the Black Captain stayed there for some days, and Barrow-wights were roused, and all things of evil spirit, hostile to Elves and Men, were on the watch with malice in the Old Forest and on the Barrow-downs.

This is in a section of summary by CT, not a direct quote from JRRT's writings or notes.
This camp was established after the Black Riders had taken Sarn Ford on the night of September the 22nd, and four riders (according to tRotK-appendix B) had entered the Shire to seek "Baggins" and the ring (Khamul was the Black Rider that had words with The Gaffer on the evening of the 23rd in Hobbiton, just as Frodo, Sam and Pippin were leaving.) The hobbits reached Bombadil's house on the 26th in the evening and stayed through the 27th, leaving on the 28th in the morning.
I have several questions about this delay of a day. How much did Tom and Goldberry know about the Witch King's invasion of the Downs? Tom says he was not looking for the hobbits, but later it is revealed that he had messages from Gildor, and possibly information from Farmer Maggot as well. Was the one-day delay on Tom's part done to protect the hobbits without revealing to them the real danger they were in? It rained all day on the 27th because it was "Goldberry's washing day." What was she washing? The residue of evil left by the Witch King? The tracks of the hobbits through the Old Forest? and, was the Witch King still on the Downs when the hobbits were safe in the House of Tom Bombadil? Was the rain a spell to protect and hide them? Why would Tom let them go to the Downs by themselves if he knew danger was so near? The Downs were clearly part if "his little land" that he would not pass out of, or he would not have ended up riding with them to the East Road. Just what did Tom know, and when did he know it?