I say, and with God's success: He is obligated to seclude for a month, any month it may be, continuously both day and night, unlike if he vowed to fast a month without stipulating continuity or intention, in which case he has the choice to either separate it or keep it continuous. The difference between them is that seclusion lasts both at night and during the day, thus it consists of connected parts, and what consists of connected parts cannot be separated unless explicitly stated. In contrast, fasting does not occur at night, thus it is separate, and what is inherently separate does not require continuity unless explicitly stated. Refer to: Al-Hadiyah Al-‘Alaiyah, pp. 185-186, and God knows best.