Orderbook historical periods

For different exchanges and symbols, I’m interested in the starting dates of historical orderbook snapshots. Is there any method (e.g., tables or APIs) to find out the starting dates other than calling /orders/snapshot API many times?

Yes, the Exchange Markets Ticker provides a first_order_book timestamp field:
https://nomics.com/docs/#operation/getExchangeMarketsTicker

That is exactly what I was looking for! Thanks!