About the 4 minutes delay. It appears to be bang on because the RDF data went through a filter station (where people examined the plotted information) before being passed to the FC bunker - this website is definitely worth a read.
http://www.ventnorradar.co.uk/CH.htm
"The edited data was assembled as markers on a large plotting table and this showed the situation as it had been something like four minutes previously : since then the bombers would have flown about another fifteen miles"
This is interesting too. Vector was only confirmed with the second reading.
"Repeated plots became the direction of travel (vector) with the height and estimated number of aircraft repeatedly confirmed"
CH was blind past the coast and then the OC was used. But was the delay resolved for the BoB???
"With the separate raids thus identified, the information was passed to an Operations room staff who could then make the tactical decisions regarding the deployment and vectoring of the defending aircraft, either those already in the air or presently on the ground, towards their ever moving targets. It was found that those best equipped to calculate the required courses were recuperating experienced pilots as they were able to better visulise the everchanging relationships between defending and attacking aircraft. However, once the enemy aircraft had crossed the coast the CH RDF could no longer detect them and then the Royal Observer Corps reports to the Filter Room became the sole means of tracking the enemy."
"The system of having to use correction charts before reporting plots to the Filter Room contributed to the four minute delay and and sometimes of course the human factor introduced errors. This problem was solved by 'The Calculator'. Designed and installed by the Post Office ( which later constructed the Colossi computers for Bletchley Park) and using relays and uniselectors, this little known and uncelebrated early form of computer automatically added the correction factors to the input plots and displayed the results visually as the grid reference. The machine could also correct heights in the same way and a mechanically linked teleprinter could send the data by telephone line to the remote Filter Room. Ventnor was equipped with its first calculator in June 1940 and received its second in April 1941."