Tomorrow I should receive mine... I am looking forward to it!
Regarding your question, this is the answer from Metrum:
In the first 3 weeks it is good to leave it switched on . In that time the sound quality will grow but especially in the first week. After this period it is good to switch it on 15 minutes before a listening session.
Danke!
A local vendor is offering this DAC, along with amplifiers they build - I purchased one of the amplifiers, and planned to take it to a show. But my Gumby requires 24 hours warm-up. I asked if I could borrow the Musette. I had it for several weeks of listening, along with the show. Really small, convenient too in that it only takes a few minutes to warm up. I would certainly have made the purchase if it weren't for my already owning the Gumby. Particularly excellent presentation of analog recordings!