So I have my IATRA exam written and passed already, however, I currently have less than 250 hours. When I reach my 250 hours (hopefully by the end of the month), will my IATRA become valid automatically, or is there something I have to send to Transport Canada to let them know that it has become valid. I wrote the exam towards the end of March of this year.

Thanks!

The exam itself is valid for 24 months. You don't need to tell TC about your hours, but try to get a Type Rating within this time frame to "lock it in"

Many operators fly a single pilot airplane with 2 pilots such as King Air and PC-12. These airplanes won't work to lock in your IATRA . You would need to get on a real 2-crew airplane like a Q400 which are certified as such.

Good luck!