Collect!

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.