In this case, the script is sleeping until the conditions become active, and checking every 1800 ticks, or 1 minute.

My question at that point was if it also did an initial check. So I either needed to wait 1 minute after all crystals were destroyed, or I needed to wait 7 minutues , 1 minute per line, for 7 lines. I waited a few minutes and it didn't work, waited 7 and it did, so my current opinion is that waiting 7 minutes covers your bases no matter which order you destroy the crystals.

The Legendary bit comes from

(if (>= (game_difficulty_get_real) legendary)

(ee_activate)

)

which occurs right when the brute and grunts spawn at the top of the cliff, past the hunters and AA turret. Which is also why I said you could technically shave some time off if you knew which crystals were dead right when this starts, since you could start counting from that moment if you knew you had already destroyed particular crystals at each minute 'check'. 7 minutes covers every order of destroying them, so I say it's the simpler way to do it (and has a nice ring to it).

As for the b_ex_has_started thing, that seems to start somewhere between the next section (with the dropship, broken warthog, prowlers, and mongooses) and the crashed longsword beyond the big trench. It triggers at a certain distance, or when certain enemies are dead, or when you or an AI is in a mongoose, so I suggested playing it safe and not even entering that next area let alone killing any of them or moving past it. Here is all the script I have if you want to search for it, it's too much to post in pastebin, you're looking for (set b_ex_p1_has_started true)