Firstly: Votive Seclusion
Whoever vowed to seclude himself, it is wajib for him to fulfil said vow. This is by agreement of the four schools of jurisprudence.
Secondly: Votive Seclusion in the Three Mosques
Whoever vows to seclude himself in one of the three mosques (al-Masjid al-Haram, the Prophet's Mosque ﷺ in Medina, and al-Aqsa Mosque in Jerusalem) then he must fulfil said vow. This is the position of the majority: Malikis, Shafi`is, and Hanbalis.
Thirdly: Vowing Seclusion before Islam
Whoever vows to seclude himself before Islam must fulfil this vow once he is Muslim. This is the position of the Zahiris, and a narration from Ahmad. It is the choice of Ibn Battal, al-Baghawi, al-San`ani, al-Shinqiti, and Ibn `Uthaymin.
Fourthly: Vowing Seclusion for a Day
Whoever vows seclusion for a day, then this does not include the night. This is the position of the majority: Hanafis, Shafi`is, and Hanbalis.