Hello
I use oestrogel (an oestrogen only gel) with a mirena coil and it didn't matter where I was in my cycle when I started it.
I would guess that it is probably OK wherever you start in your cycle with an evorel patch too unless u were changing from a different HRT that had given you a monthly bleed. And you say this is your first HRT, so should be fine if you don't exactly know when your bleed would normally start.
However, you can probably try to guess using the breast tenderness as a guide? I still have a very obvious cycle on my mirena and get very sore breasts for 10 to 14 days before I get my incredibly light period which is just a few days of mainly pink brownish spotting. On the day the spotting starts my breast pain disappears and any lumpiness or swelling goes down. If you've noticed a pattern of cyclical breast pain every few weeks, then maybe start your patch a day or 2 after it stops?
But again, I don't think it should overly concern you if don't guess it accurately.