The rule of thumb is that the five days preceding ovulation, the day of ovulation and the day afterwards would be the most fertile. LH levels and testing allow you to find the point in the cycle where you are likely to be ovulating - your peak will be within 8-20 hours of ovulation.
Some people find they can track a gradual rise in LH and others have the peak happen really quickly (I fall into the latter camp). That’s why I prefer using the easy@home testing strips because they’re cheaper so you can use them more than once a day to track your level progression. You can use the app to take a photo and it will give you a reading of how you compare to a 1.0 reading (the level where your test line matches the control line).
Often people think that you need a reading of 1.0 or over for a positive LH test result but again, everyone is different, plus the reading is affected by how diluted your urine is.
Other people prefer the once a day nature of the Clear Blue. If you have a very quick peak though the timing of the Clear Blue would have to be in sync to get you the static smiley.
Tracking BBT helps to confirm if you have actually ovulated (by seeing the temp spike) but it won’t give you pre-warning of when ovulation takes place necessarily unless you use it to map your cycle e.g. you get your temp spike consistently on Day 17 of your cycle which would mean you likely ovulate on Day 15 or 16.
One of the issues with TFMR is that women’s cycles can get thrown out by it, additionally perimenopause can start to disrupt/change cycle length. That’s why testing is helpful to understand what is happening when in an unfamiliar length cycle.
Hope that’s helpful.