Does the 2000 Honda Odyssey have a timing belt or chain?

All Honda Odyssey vehicles, regardless of year (so that includes Your 2000 model) will use timing belts, not chains. These typically have a life cycle of around 60,000 miles, though some of the newer models (Yours isn't) have belts made of kevlar, that can go for as much aS-100k miles. When You get this replaced, You can ask for that upgrade. Costs for sorting out issues here are going to be about $200 for the parts and typically $300 to $330 for labor costs. If You're comfortable in the engine, this is a repair that's not terrible to do by Yourself.