Does anyone know how long it generally takes for BTC to appear in your wallet when Mt Gox is sweeping funds?
You should be able to monitor the "sweep" transaction through Blockchain.info.
If the transaction has six confirmations, then the BTCs should be added to your Mt. Gox account. If the transaction isn't confirming, then it has nothing to do with Mt. Gox and everything to do with it not having fees paid, or it coming from a transaction which also is waiting on confirmations, etc.
If it is a "spam-like" transaction (e.g., low amount, was paid out recently, like within the past day, etc.) it can be a day or longer before a miner includes it in a block.