Everywhere is different, and with the VSAS system for some schools, the entire thing may be changing, but I startede looking Jan, Feb of M3 year and most applications were submitted late Mar-Apr. However, do not expect to hear anything for what seems like ages as most places take care of their own and do not let you know until June.
Good luck though, aways are exhausting, but if you wanna go some place specific or want a competitive specialty they are a necessary evil.
