Sounds to me you are being sensible. As you become older, you have to pace yourself more carefully and allow for recovery time, particularly if you are working part time. But you do bring maturity, understanding and experience to your studies, so while you cannot burn the candle at both ends as you could when you were younger, you have huge advantages.
Well done for choosing to embark on this new adventure. Are your studies musically related? Whatever you do, look after yourself. Leave time to relax.
On a personal note, I find it difficult to do much in the evenings, particularly if I have demands on my time the next day, but then I am over 60 and have health and energy challenges.