I say, and with Allah's success: It is recommended to hasten it, unless there are clouds in the sky, in which case the Maghrib prayer should be delayed; out of caution that it might occur before its time. For Salama ibn al-Akwa' (may Allah be pleased with him) reported: "Indeed, the Messenger of Allah (peace be upon him) would pray Maghrib when the sun had set and was hidden behind the veil." This is found in Sahih Muslim 1: 441, and Sahih Ibn Hibban 4: 389. See: Al-Wiqayah p. 137, and Al-Tabeen 1: 84, and Allah knows best.