In answer to a questioner asking whether it is permissible for a group of Muslims to set a particular night to pray communally as a form of voluntary worship, sheikh Faysal Mawlawi (a respected mainstream Sunni Lebanese scholar) said (paraphrased and summarized):
Performing qiyam communally outside of Ramadan is something the Prophet did, as is narrated by Ibn Masud in Sahih al-Bukhari and Muslim.
As for setting a specific night for performing qiyam, this is not something the Prophet did, but it agrees with his Sunna in encouraging performing qiyam, therefore it is incorrect to consider it a bidaa (false innovation) since it has a basis in our religion and has been permitted by the majority of scholars except the Hanafis.
Source (Arabic PDF): IslamOnline Fatwa