This is probably too much data for you...........but......just so you don't wind up drinking too many calories........
-at a pretty raucous 277w for a whole hour you'd burn 1000KJ (raucous for a beginner or low level amateur)
-your body typically is topped with 400-700 g of glycogen (liver plus muscle), this at 4.2KJ/g equates to about 2000KJ work using just glycogen assuming starting at 500g
-meaning you'd have to ride at 277w for just over 2 hours to deplete your body's starting glycogen
I would say if you're starting out and likely doing an hour or less, simply be sure to have your last full meal about 2 hours before. Then, a small snack with light carb some 30min before. Water on the bike. If you really need electrolyte for indoors heat, look into Nuun tablets. Those are electrolyte without adding unneeded calories. Then off the bike at end, sip some water and maybe have a small snack.
For what you're after I would:
-eat standard meal at least 2hrs before
-hydrate normally before during day
-small snack with a little carb before workout (maybe a Kid's Cliff Z-bar, lower calorie and carb, but has something)
-Nuun tablet in your water for the ride
-hydrate after, maybe a light snack to stave off cravings later
By all means, don't go for the carb amounts in many full strength sports drinks or "race day" drinks.
Good luck!