People underestimate how fast the Victorians could move things. There were no cars, so they had lots of trains instead - way more train lines than exist today, with much cheaper and more frequent services, because everything moved by rail so that was where all the investment went. This was the height of the industrial age, after all. And since there were no (or not many) telephones and no internet, they had multiple mail deliveries every day, because all communication was done by mail or telegram so that was where all the investment went. They had a same day mail service, even.
I'm not exaggerating about that, btw. My great-grandfather collected postcards all his life, starting as a little boy in Norfolk in the early 1900s, and among his collection is a postcard sent by a cousin who lived way up north. She posted the card first thing one morning saying that she was coming down by train to see her aunt and would be arriving at just after 3pm that afternoon - the same afternoon she posted the card. The card literally says 'this afternoon'. Posted first thing, and it arrived in good time for her uncle and aunt to know they needed to meet her off the train at 3pm that same day - and she knew posting it that it would arrive in good time. Same day delivery, and that was something like 1905.
Flower shipments from the Netherlands to London in that same era was a booming business, that's how all the markets were kept supplied. So yes, van Helsing could get flowers delivered overnight on a daily basis.