We strongly recommend that you use a true bitcoin wallet for spending to avoid delayed transactions, but you will be able to use any service compatible with Payment Protocol. (blog.bitpay.com)
When fees are high, users can often save money by delaying transactions to quieter times like late at night and the weekend. (cryptoninjas.net)
Many users complain of slow or unresponsive customer support, delayed transaction times, slow ID verification, etc.. (captainaltcoin.com)