I bought some BTC on Coinbase last night and had it sent to Poloniex. I know the BTC wallet address was accurate. Its still pending 11 hours later and doesn't show up in the Poloniex deposit/withdrawal history. Any clue on how long BTC transactions are taking?
Sometimes its take much time to be the transaction will process. That's normal sir that its pending in 11 hours because I tried poloniex also. There some times that they pending your bitcoin. If you can cancel it, please cancel it then try to do it again but if you cannot cancel, may be you should wait upto 10 days and past a ticket to them. I say that because I experienced that already.
Maybe you need to find another btc wallet that is not delayed in their transaction, you can try xapo or blockchain, you must use trusted bitcoin wallets and those wallet that are not having some problems like that, here in the Philippines, coins.ph is not delay, sometimes it is delivered ahead of time, they have a fast transaction.