with no specific knowledge of delta's hiring policy, i think it's safe to say that you will not be told on the spot if you are or are not hired. this is not common practice for most fields, so unless you really screw up the interview and they are not interested, your interview will likely end with a polite "thank you, and you can expect to hear from us in a few days."

also, the amount of time between your offer and your start date would likely be more up to you than up to delta.

again, this is just a general observation and not based on delta policy