Does the absolute preference for prayer mean a Muslim may spend all their time in it, with the exception of the forbidden times, which are spent in Quran recitation and remembrance of Allah?

Prayer is the best physical act of worship, but performing it at all times is not absolutely the best. A less virtuous act of worship performed at its designated time is better than a more virtuous one. For example, glorifying Allah (Tasbeeh) in bowing (rukūʿ) and prostration (sujūd) is better than reciting the Quran, and supplicating (duʿāʾ) at the end of prayer is better than reciting the Quran. Sometimes a person might find an opening in a less virtuous act that they do not find in a more virtuous one, or it might be made easier for them, making it better in their specific case. The best acts of worship are those that conform to the guidance of the Prophet (peace be upon him) and his Companions. One should undertake acts that can be sustained, for the best deeds are those that are consistent, even if small. A little that is constant is better than a lot that isقطع. A less virtuous act of worship might be better at its specific time, such as seeking forgiveness (istighfār) at dawn after the Witr prayer, which is better than a supererogatory prayer, due to Allah’s praise for those who seek forgiveness at dawn.