it will take as long as it needs - getting out of the door is the hardest part.
everyone has different approaches to what they think is the best time of day to run - some of us prefer morning, others evening. once you adapt, you will muster the energy to get out and for me, running in the morning is easier and it's usually quieter as well.
and depending on how far you plan to run, you don't necessarily need any pre-fuel drink/food if you've eaten and hydrated well the previous evening. I'll happily do an hour's morning run on no fuel or drink.
anyway Brighton marathon doesn't start until 9am - that's almost afternoon.... 