The opener isn't a fixed thing. You adapt it to each fight.
But the idea for that "optimal" thing is as follows: Triple saves the most time in F4s if it's not under Ley Lines. The relative gains in comparison to the gcd are the same on either case, but since your gcd is longer outside LL, you save more absolute time that way (Triple shaves you ~1.2s outside LL and only ~0.9s in LL). So to get most out of Triple, you use it first and weave LL at the end. If you do it that way, the cds will always line up so you can Triple>LL.
To use LL earlier, you have two options:
You B3>Eno>T3>LL, this having animation lock (wasted 0.5 secs or so) or you do it prepull. Note that the only spell that gets any benefit here is B4, and that probably cancels out with the animation lock for LL compared to what I suggested.
Since B3 is cast prepull, it has technically a cast time of 0 seconds (the cast is channelled before the fight starts). This means that if you opt for this, you're wasting LL timer on a spell that has no cast time (which means that, in all likelihood, with the 0.5 seconds of animation lock, you may miss out on two LL spells).
Further, both of these options also do not benefit from the "optimal" Triple usage (that saves you the most time over the course of a fight).
Using it like that also makes everything end up weaved nicely, and you only waste like 0.2s of pot time (probably irrelevant).
This said, in some fights it's worth to have Triple and LL overlap- namely, Susie EX p3. This way, you use Triple to move to the correct side for Levinbolts, and use Between the Lines to get back to the previous side. It's technically wasting a bit of the dps potential of these cds, but it's better than walking without casting anything for 1s.
If you have mana for 6x Fire IV, you'll have mana for Foul when you hit UI.
If you have Sharpcast, you do F4x2>F>F4x2>Firestarter>F4x2>B3>Foul (you have enough mana if a Fire consumes the UH, and you can afford to do that with Sharpcast because you get a Firestarter to refresh AF).