Are you saying that it's not wise to move to part time once the orientation period is over due to the intensity of the skills required on the unit?
I would say yes.
If you signed a contract that states you must work a 40 hour week, changing this will be very difficult. Your manager may not fully disclose this at this point because they may not want to lose you as a candidate, but changing your hours wont be easy, and probably not fair to you (see the quoted statement).
Here is another point to consider...the PICU has its highs and its very lows. If you are not 100% committed in working (anywhere for that matter), what will happen when you hit a very low (your patient dies, you get reprimanded, you make an error, etc). Will you want to leave because you have the luxury to do so? On a unit that often has 1 to 1 nurses, one nurse leaving can be a huge deal. I dont question your desire of working in the PICU, i am just wondering about your commitment to working.
There are days when we dont want to be working, but most cant stop because 1) they need to work, the $, and 2) they really truly are committed to their jobs. Its a mixture of the 2 that carries everyone through their rough times.
Whatever you decide though, good luck!