Shaykh al-Arab wal-Ajam Hadhrat Haji Imdadullah mohajir Makki (Allah have mercy on him) instructs a seeker,

‘After fulfilling the faraidh (absolutely essential), wajibat (highly recommended) and Sunna one should occupy his time in spiritual works of rectifying the condition of his heart (remembrance and contemplation) and not spend it in offering extra (nafil) salah or recitation of litanies. Instead he should consider the rectification of his heart to be a perpetual must (fardh) and never be negligent in it.’

Dhiya al-Qulub via Taleemud-deen, page 45