i suppose for quick exchange and payment you have to visit the exchanges used by miningpoolhub (dove wallet, bittrex and poloniex) and see what pairs are being traded. if the pair you chose is not traded there, maybe you will have to wait. in any case an answer from miningpoolhub would be better to clear things about autoexchange issues.
Do you mean the pairs shown on the auto-exchange page on MiningPoolHub? BTC and XMR are both supported on Poloniex, and there seems to be active trading on the exchange between them. But yeah, it would be good to hear directly. The BTC withdrawal fee is very high right now so these issues must affect a significant number of their users moving to exchange another coin.
Yes ! But you said your pair is supported so it is something else delaying the exchange. Maybe the fees as you say are very high and they want to accumulate more coins before sending them to external exchanges. We can only guess about the delay issues, that's why a direct answer from them would be best in your case.