Praise be to Allah.
Shaykh Muhammad ibn Saalih ibn ‘Uthaymeen (may Allaah have mercy on him) was asked this question, and he replied as follows:
Setting aside a regular day for giving lectures or holding a study circle is not a reprehensible bid’ah. Rather it is permissible, as it is permissible to set aside a day in schools and institutes to study fiqh, tafseer, etc. Undoubtedly seeking Islamic knowledge is a form of worship but setting aside a particular day for it is something which is dictated by our circumstances. It is in our interests to set aside a specific day for that so that people will not be put in a difficult position. Seeking knowledge is not an act of worship which is linked to a specific time, rather it is to be done at times which are convenient. But if a special day is set aside and is regarded as being solely for seeking knowledge, then this is bid’ah.
With regard to a group agreeing to meet on a specific night for qiyaam al-layl, this is bid’ah, because it is not prescribed for a group to perform qiyaam al-layl together. But if this is done occasionally and unintentionally, as happened in the case of the Prophet (peace and blessings of Allaah be upon him) and ‘Abd-Allaah (may Allaah be pleased with him), this is OK.