You can type affirmations any time of the day. Early morning is a particularly good time to type your affirmations. Also, it is beneficial if you can have an autosuggestion session before going to bed in the night. Especially so if the issue you are dealing with is about sleep or dreaming.
Whatever schedule you are following, see to it that you are calm and relaxed before beginning the session. If you are a bit disturbed, practise physical relaxation before you begin the Autosuggestion session.
It is also a good idea to start your session with affirmations of relaxation like ‘I am relaxed and calm‘ before beginning the session for the actual issue at hand.