Well, it's probably best to eat they way you always do before a ride if it floats your boat...As a trainer, I'm always telling clients to look a day before and after an event. Junk in/junky preformance.
The day after can become a burn-out too if you don't take care of your needs the day prior. Plus, the day prior to the ride, good balanced nutrition will help all your cells hang in there together.
The day after the ride is when you might find yourself dehydrated (you can really sweat till your wet in spin) or have some lactic acid in the quads/calves from preforming at a higher level than normal, along with being really tired from the exertion.
Good times!
On a serious note, in the book, "Physiology of Sport and Exercise" one study shows that athletes who train intensely and eat low-carbs (40%) often experience a day-to-day decrease in muscle glycogen. Those who ate high carbs (70%), their muscle glycogen levels recovered almost completely within 22 hours of training. So, you see, it's not just the food you eat a couple hours prior; it's the day before and after so that you can get up and go again and again without getting run-down.
The time of the day for the ride sounds harsh to me, too...
...perhaps keep in mind that you have all day to enjoy good food as a plus; the down side, is after the spin class you'll want to drop into bed earlier than usual; it might throw your sleep cycle off. You can off set your desire to crash out immediatly by trying to stay awake (HA!) until your usual bed hour...or you can knock your self out with a PM formula (Exedrine/Tylonal). Sleep is REALLY important to endurance sport-related recovery and endurance.
Balance is the key to the preperation...sound sleep, balanced meals (70% carbs), good attitude so that stress doesn't burn you out during the day and lots of water/electrolites.
Terry