بسم الله الرحمن الرحيم
It is better that the whole Quran is recited in one week or at least in forty days.
وندب لحافظ القرآن أن يختم في كل أربعين يوما حزب وثلثا حزب أو أقل . (الهنديه: 5/317)
Hadhrat Shaikh Zakariya has written in Fazail Amal with reference to Imam Abu Hanifah (may Allah have mercy upon him) that it is the right of the Holy Quran that it is completed twice in a year. (Fazail Amal: 14) Thus one should try to complete Quran at least twice a year.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.