First time (before permanent move to Canada but after soft landing): I applied after soft landing as i needed proof (COPR doc) that i will be moving to Canada and travel daily to US for work.
Application got returned with a letter for requiring 3 years continuous stay as i was completing 2 years continuous stay in US in 2016.
Second time: I applied after 1 year stay in Canada (apart from 2 years in US) and got the card.
I think that one can try before even landing as we have the visa/approved PR anyway, to avoid waiting for landing. Even if they reject the application then we can apply again as they return our check
.
(I applied via paper instead of online because there was some PR card number or some other number was required and it was not accepting in certain format hence thought i would send paper application).