Count Dracula

Lucy Westenra's sister Mina bids farewell to her fiancÃ© Jonathan Harker, who is leaving for a business trip. Harker, a solicitor, is travelling to Count Dracula's castle in Transylvania to expedite his purchase of Carfax Abbey and other properties in England.
At the door of the castle, Count Dracula himself welcomes Jonathan. Abandoned by superstitious locals, Harker was forced to accept a lift there from an anonymous passing coachman. Jonathan agrees to stay for a month to help the Count with his English. Dracula is urbane and gracious, but also vaguely sinister, and casts no reflection. After a series of disturbing events, Harker explores the castle, finds the Count asleep in a coffin, and tries (ineffectually) to kill him with a shovel.
In England, Mina and Lucy go to the seaside town of Whitby. Among their friends are Quincey Holmwood (Lucy's American fiancÃ©), and Dr. John Seward, who owns a local asylum. Among Seward's patients is the madman Renfield, who worships and fears Dracula. Mina and Lucy witness a storm in which the foreign ship 'Demeter' goes aground, and later a local is found dead. Mina follows a sleepwalking Lucy to the local graveyard and glimpses Dracula holding her in his arms. Lucy thereafter grows pale and weak; at night in her bedroom, Dracula drinks her blood. Jonathan meanwhile turns up delirious and weak in a convent in Budapest.
Seward calls on his friend Abraham Van Helsing for help with Lucy's strange illness. Although Van Helsing recognizes the symptoms and protects her bedroom with garlic, a wolf shatters the room's window; the shock kills Lucy's mother, and Lucy is found pale and nearly dead.
Seward and Holmwood both accompany Van Helsing to Lucy's grave. A bloodied Lucy approaches, and attempts to entice Holmwood, but is forced to flee from Van Helsing's crucifix. Later in the tomb, Holmwood drives a wooden stake into Lucy's heart. Van Helsing fills her mouth with garlic and cuts off her head.
Harker, Van Helsing, Seward, and Holmwood all go to Carfax Abbey to sterilize Dracula's refuges - boxes of native earth - with Christian artefacts. Renfield realizes Dracula is now visiting Mina, and seeks to warn her and Dr. Seward. In revenge, Dracula kills Renfield, who just manages to warn the others. They rush to find Mina in her bedroom, drinking blood from Dracula's chest. Dracula vanishes as they enter. Van Helsing touches and sears the hysterical Mina's forehead with a piece of communion wafer, which scars her until Dracula dies.
The Count flees back to his castle, and they follow; Van Helsing and Mina go to the Castle, while the others follow the Gypsies transporting Dracula's coffin. In the Transylvanian wilderness, Dracula's brides attack Van Helsing and Mina, but Van Helsing thwarts them, and destroys them the following day. Harker, Seward and Holmwood chase Dracula's carriage and fight the Gypsies loyal to Dracula; Mina shoots one, saving Harker. The pursuers reach and open the coffin; inside, Dracula smiles, because it is almost sunset, but Van Helsing drives a stake into the vampire's heart, and the body disintegrates, leaving only his clothes and ashes.

Question: How long does Jonathan agree to stay in the castle?
Answer: a month