Apple Watch Series 8 Resting Heart Rate Accuracy Issue

I am wondering how the resting heart rate calculation on the Apple Watch Series 8 is at all accurate. I’ll check it and some days the last reading taken was 9 am, other days it will do it’s last reading at 7:30 pm, yet other days the last reading is at 11:40pm.

How can it be accurate if it is not taking readings multiple times throughout the day or at least near similar times? I understand it is based on when you are resting and you’re not always resting at the same times every day, but my HR tends to be higher at night so if it’s last reading is in the AM, how can it be accurate? Also, I know there are plenty of times I am at rest watching TV in the evening but it still will have the last reading at 9:40 am so it’s not taking my other resting rates into account.

Please explain.