bruhaha more or less outlined what happens on a high level pretty closely. There are some minor variations/additions what happens on the NK ops spec.

It takes a bit longer usually than 2 days for the frame to enter the spec here. The down time between the initial arrival of the aircraft and EIS is a pretty standard timeframe set to create a buffer in case anything goes wrong in which case you have to go fishing for planes, usually at the expense of a spare. Its best to have a more conservative plan when it comes to this stuff which more often than not allows for "soft testing" to rotate the aircraft through a few times before it is really needed to pick up its scheduled lines of flying.