You do not need to worry about refueling during an exercise session of less than an hour. More than two hours you need to start considering it. So somewhere in the middle you need to start listening and find out when YOUR body needs it.
There are many gels, gu-type goos, chewables and water additives that you can take to get in the needed calories. You absolutely do NOT want to drink a litre an hour! You'd slosh! Find your own water intake level that keeps you personally feeling comfortably not dehydrated, but yet also not sloshy.
When I did my half (2:45 - I'm slow), I alternated a cup of water with a cup of water+Leppin at each of the four water stops. So in those nearly three hours I had about 3-4 cups of water (small cups, not 8oz), and no actual food.
I can't run and chew. Just can't do it.
Deb, in New Zealand