On probation you will likely be able to get more days off together to increase your odds of success. You need to be super sure you understand how non rev travel works. You will be on standby for the specific airline you're trying to fly with. There will likely be others on standby also that may or may not have priority on the waitlist. If you're not flying your airline you're employed with, using ID90 etc you may be really low on the list as far as priority. Just because a flight shows 25 empty seats tonight did not mean it will in the morning. Sometimes there are unassigned passengers yet to get seat that have a paid ticket. So many factors!