Great ideas can't be scheduled. They will come at any time - night or day.
The key is to have a way to collect them all. A plugged in iPhone works: "Hey Siri! Remind me to..." (Mind you - the key is to say enough that - even when you have the inevitable mistranslated word - you will still get the idea).
The idea grabbing tool that I like most of all is a four color pen and a moleskine notebook. You can leave one on the nightstand by your bed. You can get a small one that fits in your pocket. Wherever I am, and whatever I'm doing (the exception to this being driving a car) - I can write down an idea in blue ink (that's the color I choose for my ideas). Additionally I circle it in red or put a side note "PROCESS THIS IDEA" in red (that's the color I choose for my follow ups).
I once read that an idea will stay in your head for an average of 30 seconds. Then it's gone. Capaturing is the key. 30 seconds sounds a little long actually - capturing and collecting is the key.