Jonathan Harker knows the count is creepy and there's something about his manner that he finds repugnant, yet he's there on business and decides to be patient and polite until the count allows him to leave the castle. On May 19 when he disobeys the counts order not to fall asleep anywhere but in his own rooms, Harker experiences the three "sisters" who want to drink his blood until Dracula shows up in the nick of time and furiously pushes them away and forbids them to drink Harker's blood until he's finished with him.
The following day, Dracula has Harker write the three post-dated letters to his friends and family to assure them that he is alive and safe and, according to the final letter, on his way home to England. He realizes the date of the third letter is the date when the count will allow the three females to drink his blood and he will never be allowed to return home.
Harker's next entry is nine days after the May 28 entry to report his failure to get the Szganys, gypsies who set up camp outside the castle, to post two letters for him. Dracula intercepts the letters.
I don't understand why Harker doesn't try to escape when he knows his days are numbered and he's going to be drained of blood by the "three sisters" until he's dead. In fact, his next entry isn't until May 31, nine days later, when he realizes the count stole his suit and all of his stationery He sees Dracula scaling the castle wall to get out, so why doesn't he try this sooner. What does he have to lose? Especially when he knows the vampires sleep during the day and are helpless to pursue him until dark. The wolves don't seem to be around unless the count is awake either, so he could get through the woods.
His next diary entry isn't until June 17, more than two weeks after the last entry, when the Slovaks arrive with the empty coffins, almost a month after his experience when the three female vampires want to drink his blood.
He does crawl to the count's window and searches the castle until he finds the count resting in his coffin, but is too afraid to search him for the key. Instead, he flees to his room. You'd think he would either crawl lower to get out of the castle or search for a lower window to escape from. There had to be some way for him to escape instead of just sitting in his room doing nothing for over a month waiting to die.
What did he do all those hours and days and weeks sitting alone in that room with nothing but books? How could he focus on reading books when he knew a violent death was getting closer and closer? He had all those daylight hours to figure out an escape plan and put it into use, but instead he sat helplessly hoping for some outside circumstance or visitor to present itself that would give him a chance to escape.