It all depends on your facility's rules, like Jaynie said. At my facility, you don't have to wait for an opening to change your schedule hours, but you have to work whatever has been scheduled already, so it could up to a month or so to get changed around entirely--not a fast process if it's something you need NOW. Also, some advice from a NOC CNA like myself: don't change to this shift simply because you think it's "easier." It's not. There's a ton of "baggage" with NOCs as there are with the other shifts. For instance, one shift takes two days of planning (when will you sleep before the shift? when can you sleep after? do you have other commitments during the day?), you're stuck there until your relief arrives (like other shifts, if your replacement doesn't come in when scheduled because of poor planning or overlseeping or whatever, which has happened to my replacement several times as she isn't the most reliable, you might not get to leave right away--what will you do then?), and AM cares can be incredibly stressful (at my facility, I have to get 5 residents up, but I have less than two hours to do it or I can't get my last rounds done--and one lady can take up to an entire hour to do because she is so resistive to cares! Also, call lights are going off and one time, my 104-year-old resident fell at 6:30am and of course that became my priority, but you can imagine what it was like to then have to listen to all the complaining from the day girls when two other residents, one who needs assistance only with bottom-half cares and does the rest herself, were not up yet and I had to leave exactly at 7 because management is super strict about not going over hours...NOC/AM shift change is super dramatic at my ALF, but it was like that when I worked NOCs at a LTC last year as well, so...).
Also, at my current facility, NOCs are also responsible for cleaning the bathrooms (we have five) and doing all kitchen work (cleaning, cooking/baking, preparing drink trays for breakfast). It's busy, don't be fooled. There's only two of us on my shift, and because it is a small (40 res) facility, we don't have a RN on site! So compared to my LTC job, it's nice because you don't have the addes pressure of being watched, but also it's stressful--for example, last night my 104-yr-old resident was having heavy rectal bleeding. No nurses around for something like that...it's hard! But we have an extensive 'emergency plans' for things like that (when to call 911, when to call our DON, when to call families, etc) and the facility runs smoothly.