I usually don't think of it until it's almost used up. Around 5 minutes or less left, and all too often not until I get the message that I could eat another bite (i.e. it's duration is gone completely).
I have food to waste too....like way too much food. I like farming and grinding so I tend to over-gather everything, especially food. So, I'd prefer if I thought of it when it was somewhere between 50% and 20% duration left. But I simply don't.