We have already prepared pre-mixed bitcoins (or other coins) for you. All you need to do is fill the form containing list of your outputs (the address where anonymized coins will be sent) and send required amount of coins to our address. The mixed coins will be then sent back to you automatically. You can send any number of transactions to our input address. Your coins will be used in future for mixing also.
It's up to 24 hours. Usually it's almost instant, depends on service load.
The way bitcoin or any other public-blockchain transactions work causes them to be chained together in a permanent public record. They are traceable along the blockchain from one crypto address to another. A mixing service can be used to mix one's funds with other's, with the intention of confusing the trail back to the fund's original source. Therefore, bitcoin (or other coin) mixing service helps protect privacy of your bitcoin transactions.