Hi, I am a medical physics student who has done a fair bit of research by this. To my knowledge, applications commence in January, and then over the next months you find out if you are long listed, shortlisted and invited for an interview or placed on interview reserve list etc..
The national school change the application quite a bit each year which isn’t entirely helpful! But if you browse the websites previous application dates, you can see when offers where handed out for specific programmes!
Previous year competition ratios are also available to look at!
For standing out, I’d recommend attempting to get work experience with your local hospital in the department you’d like to apply for, and generally show an interest in this field outside of your studies!
Best of luck!