Ok, I'm not an expert on trains in the 1800's, but today it can take 1 hour 45 minutes to get from London to Derbyshire on the fastest trains, so I'm thinking 3 ½ -4 hours back then. Also, if I mention a station that didn't exist then, I apologize.
P.S. I'm going from the books AND Jeremy Brett's Sherlock Holmes
Holmes dashed around our apartments, gathering items he deemed necessary for the errand. Lord Ackley had left for his home in Hertforshire soon after he gave us his account, or rather the account of his son-in-law, of the events the surrounded Lady Mary's death, with our assurance that we would attend to the matter directly.
"Do you think Lord Alcott killed his wife?"
"My dear Watson," Holmes sighed, "How many time must I state this: data, data, data? There's no use in making conjectures without all evidence in front of me." As Holmes and I left, bags in hand, I gave a thought to Mrs. Hudson's reaction to seeing the shambles her taller tenant had left the room in. In fact, just as we said our goodbyes to the Landlady and left the house, I fancy I heard a cry of 'Mr. Holmes!' from the second floor. From the corner of my eye, I just barely perceived a smirk upon his face as we stepped up into the cab.
In the end, we had to bolt for the moving train; the hansom we'd ordered, apparently, was driven by an Italian. Not only did he never pause for other carriages, but the driver seemed to forget completely where King's Cross was located. That is, to say, he went the wrong way and wholly refused to listen to our directions or permit us to leave his carriage.
It was an experience that even Holmes is loath to repeat.
Once we were well secured in a car of our own, I set about propping up my leg, for it had been jolted when we made the final mad leap for the train, and leaned back with a pencil and my notebook, ready to compose the story of our last mystery. I sat there for some time; the last case had been quite entangled and I wasn't quite sure where to start. When the client arrived? When we first grasped the edges of the case in the evening paper?
"You,"
"Are not about to tinge an otherwise proper series of lectures focused on the facts with romance?" I interrupted him, sprawling the first words across the page, "I am, actually." Holmes gave me an almost incredulous look before turning back to his paper. Feeling rather smug myself, I continued to write out the particulars of our last case.
"What do you think, Watson," Holmes mused, "could cause marital murder?"
"Adultery," I paused, thinking, "money, hatred, fear?"
"Yes, yes, but why murder? Why not divorce?"
"There's always a fear of scandal, perhaps of retribution on the family's part." Holmes shook his head, not satisfied with my answer.
"No, no, a spouse is always the first suspect, and in murder there is always scandal. Why commit such crimes when you know YOU shall be, at least for a time, ridiculed by the family, police, and public?" I put aside my pen and book, then sat back.
"But they're not always caught, not right away. Do you recall the singular account of 'The Eligible Bachelor'?" Holmes scoffed.
"I do indeed," a dark look passed his sharp eyes, "A hard man St. Simon was, and for Lady Helena to have survived! It was one of our more grotesque cases."
"Certainly, he had one wife killed, and got sympathy, one declared insane, and received nothing but sympathy, and one disappeared, though that wasn't of his doing,"
"And got sympathy." Holmes finished, catching my pattern, "I am glad Lady Hatty wasn't truly married to that man, though I am loath to call him so."
"Quite. She may have, one day, become one of his victims." After a moment of silence, I deemed my interrogation over, though, in truth, I enjoy that he values my opinion and wrote for the remaining three hours. I had sincerely hoped that this case wouldn't be as grotesque as the 'Bachelor'.
My hopes were never answered.