If school is what is holding your plans back, why not transfer the miles now and book at a time when school isn't an issue?
Either way you'd be hard-pressed to really do the park even if you had the entire day from open to close, definitely not worthwhile for a couple hours.
+1. If a trip to Cedar Point is a rarity for your party, then you should try to make the most of it. Attempting to fit all of this in one day is a tough challenge...unless if your "young cousin(s)" are under the age of ~12, then they might not find very many attractions suitable for them. However, standing in 1-2 hour lines in the sun for roller coasters might take a toll on your body, especially if you need catch a flight out of CLE later that night.
Some hotels in the Sandusky area offer "Stay & Ride" packages for individuals and families.
Drug stores and grocery stores in the CLE area (ie. Drug Mart) usually sell discounted tickets for the park typically $6-$10 cheaper than at the gate, but that won't get announced until we get closer to the operating season.
ProTip: If you DO plan on commuting back and forth from Cleveland to Cedar Point, look at Google Maps (or use your GPS) and plot a course using the Rye Beach Road (west on US 6) exit and then turn right on to Cedar Point Road. You'll take the back way in and save 15-30 minutes each way by skipping the Sandusky and Cedar Point Causeway mess in the morning. Plus you'll get an awesome drive along the lake shore. All of that is moot if you plan on staying at a hotel in Sandusky though.