When you are tired or sleepy your conscious mind is more passive, and your subconscious more receptive/active, which is actually the ideal state to be in as beliefs are stored and recorded in the subconscious mind.
We recommend clearing and programming in beliefs either shortly after waking or right before going to sleep as this tends to give better effects due to the above mentioned phenomenon.
Furthermore, if you clear the beliefs before bed they have much more space to integrate while you sleep. If you prefer, you can do them in the morning as you start your day as well, which gives you more space to focus on the positive beliefs consciously throughout the day.
Either way, they will be effective whatever time of day you do them, so do what feels best for you. However, you may notice better effects doing them before or after bed.
As always, we recommend experimenting and using your intuition to guide you in selecting a time.