If you're confident to your calculation you can do so. I have 5 days buffer and get new card normally. But if I am you, I will apply it four months before my earliest trip, or if there is no planned trip, wait until your card expires.
You probably would be fine to do so, but any error would cause an issue or delay. So most here suggest some 'buffer' of extra days.
How many? Let's put it this way - depends how many trips abroad you have and how complicated departures are, etc. And how confident you are.
But the way I'd look at it is: each extra day of buffer has less value. A few days extra -quite valuable if you've made a minor calculation. A week - more valuable but not as dramatically. Etc. My guess - 30 days extra probably enough for most, difference between that and 60 days actually not so big, beyond 90 days (i.e. 820 days + in Canada) - probably close to zero additional benefit for most.