On YouTube you will find extensive advice on learning classical singing. For instance, this warm-up exercise is one of many vocal training trips from 'expertvillage', a sub-site for education and training. For more of the 240 postings (as of the date of this Blog), visit this community: YouTube/classical singing.
I present this example 'as is ... where is'. I am a singer, not a vocal coach. Accordingly, I am not willing to vouch for the accuracy or reliability of the advice presented on this particular example.
For instance, on the YouTube site, someone commented about the warm up example:
Not sure if I agree 100% with what she's saying. If you're using you're voice properly and singing or speaking from your mask there is no need not to talk to keep your vocal cords "fresh." As far as when you wake up, yes your muscles are relaxed and do need to wake up too, but instead of waking up earlier and not using them, you should do some warm up vocal exercises such as humming for proper pitch placement and tone focus.I advise that you discuss the advice with your vocal coach, and write a comment on my blog (or the YouTube site).