If you are really keen to start before you're actually TTC, I might consider temping for the month before you stop your pill. It might not be totally accurate, as your body may respond to your own natural hormones differently than it does synthetic hormones, but if it gives you some sense of when you might ovulate the next month, when you are actually TTC, then it's not a terrible thing. I would just take that month of data with a grain of salt and be alert your first month of TTC to other things, like cervical mucus, to give you a better sense of when you're fertile in addition to your temps. I wouldn't temp any more than that though. It's a bit of a hassle and not worth stressing over if the mini pill means your hormone levels don't rise and fall the way they might in a natural cycle (meaning you might temp and see it looks funny and then stress about actually TTC, which might affect your fertility).
I stayed on the pill (regular pill, not the mini pill, so I wasn't ovulating) until I was ready to TTC. Came off and started to chart that first month (temp and CM) and had a totally normal fertile cycle. I found the information I got about my fertile period from that one month of charting to be really helpful. Then the next month, I planned TTC around my estimated fertile period, based on when I was fertile the month before, and used cervical mucus as a guide as well to confirm it was coming. I got pregnant that 2nd month, after only a month of charting and after 12 years on the pill before this. I think if you don't stress about it and overthink it and you really prioritise timing things around your fertile days, you won't need to be temping for months in advance to get a sense of when you're fertile. So I personally wouldn't bother. I'm doing the exact same this time, staying on the pill til we are ready to TTC and then starting to chart after.