What is the duration for which one should continue reciting Du'a al-Qunut during calamities?

Reciting the qunut in obligatory prayers is permissible during calamities, and it continues as long as the calamity exists, ceasing when it ends. This is based on the Prophet's (peace be upon him) supplication: "O Allah, save Al-Walid ibn Al-Walid. O Allah, save Salamah ibn Hisham. O Allah, save Ayyash ibn Abi Rabi'ah. O Allah, save the weak believers. O Allah, intensify Your grip on Mudar. O Allah, make it years of famine upon them, like the years of Yusuf." He then stopped it when its cause was removed. Sheikh Ibn Uthaymeen, however, was of the view that it should continue for a month and then be discontinued, even if the calamity persists.