There are rules that govern ACH reversals. My understanding is that reversals are permitted in cases where the amount transferred was incorrect or the transfer

There are rules that govern ACH reversals. My understanding is that reversals are permitted in cases where the amount transferred was incorrect or the transfer was not authorized. As another poster on this thread noted, Coinbase's terms of service appears to give them great flexibility in processing transactions. The OP, on the other hand, seems to have the understanding that Coinbase was obligated to complete his transaction within a very specific period of time. This is a dispute between two parties to a transaction. One is arguing that his counterparty failed to meet its obligations; it appears the other has the ability to argue that under its terms of service those supposed obligations never existed. Given the amount of money involved, either party might be motivated to resolve this matter through legal action. Again, this is all an inherent part of the wonderful world of counterparty risk.