Firstly it has been shown in past studies that Creatine supplementation will attenuate increases in plasma ammonia and hypoxanthine during intense endurance exercise lasting 1 hour. So it seems reasonable to suggest that Creatine supplementation may indeed improve muscle energy balance during such exercise - it's worth testing.
The authors report that Creatine supplementation significantly increased muscle total Creatine, however no difference was seen between treatments after the first 45 min of exercise. They conclude that "raising muscle
total Creatine content before exercise appears to improve the ability of the muscle to maintain energy balance during intense aerobic exercise, but not during more moderate exercise intensities".
Title:Creatine Supplementation Reduces Muscle Inosine Monophosphate during Endurance Exercise in Humans.
Authors: McConell, Shinewell, Stephens, Stathis, Canny and Snow
From: Department of Physiology, Monash University; Department of Physiology, University of Melbourne;
Exercise Metabolism Unit, Centre for Rehabilitation, Exercise and Sport Science, Victoria University of Technology; School of Health Sciences, Deakin University.
Source: Medicine & Science in Sports & Exercise; Dec2005, Vol. 37
Issue 12, p2054-2061
My take on this is that Creatine supplementation appears to work in maintaining a balance in the ATP cycle during the intense 1 hour efforts that have been tested. This sounds like an A or B grader may benefit in a 1 hour criterium, for example. They may have more energy freely available at the end of the race and secondly (my guess!) may recharge quicker afterwards. However there's no benefit below one hour or at moderate rather than intense efforts. As always, tread carefully if you try any supplementation - and seek a wide range of advice beforehand.