ideally you should use them every 45 mins with water. If you are using an electrolyte sports drink too, then the two conflict and you should use the gel less frequently. if using 2 bottles, water in one, and an electrolyte sports drink in the other for use in the last third of the event. a 60km mountain bike race might be quite tough and slow, and energy replacement/management is part of your battle plan. some use bananas, some use potatoes, fruit cake, energy bars. You need to train the way you race, thus practice with all sorts of things to find what works for you, everyone is different. A 60km road race is over before you know it, so energy drinks may well be sufficient. longer road races, switch back to the 45min gel water rule, with an electrolyte sports drink for the last third of the race.
