BBT advice

Hey ladies..

So I took a test and it’s negative and feeling very PMS symptoms(due AF in 3days) so I’ve just ordered a bbt thermometer and was just inquiring as to does it have to be the same time every morning. Or does it matter if it’s like 20/30 mins difference as I can wake anywhere between 7am - 7.20am, so like one morning I wake before my 7.20 alarm at 7 is that okay or does it have to be bang on?

Ordered ovulation sticks too to coincide with bbt

Be my first cycle since my MMC so mainly want to confirm ovulation is back on track ❤️

Any advice would be greatly appreciated