Check your cervix once a day and at the same time, it is always up and down in the day ie when you need a wee, poo etc it changes even then ( I have been cervix checking for years!)
The best time is in the morning.
After Af is finished its usualy middle/low alogn with dryish/creamy cm and as you approach ovulation it gets higher and your cm becomes much more watery and then hopefull as your cervix starts to open you will have watery/ewcm
The time between watery starting and your O opening is optimum conception time.
Though if you have had sex the night before without using anything youcant rely on your cervical checks as the cum makes your cervix soften and it will feel slightly open, its best to check cm on those days later on in the day and not rely on cervical changes and just continue the day after.
When you are oving though your cervix will still feel very open and wet in the evening, but if your having cm problems you wont nothice too much cm, just the O feeling more open, bare in mind you will still be very fertile.
After Ov your cervix closes, it feels tight again, but sometimes it takes a few days to close but more oftem than not it will close next day after ov and your cm will probably become thick or dry up.
But also remember every cervix is different!
You cant reply on cervical changes until you have done it for at least 4 or 5 cycles to get to know your pattern
But what I have wrote does genrally happen for lots, but that only on good cycles, if your stressed etc, it will be harder to tell what is going on