As I understand them, ranks can be understood as a measure of the narrative weight and focus of an endeavour in the protagonist story. They can be seen as the actual time they take in the narration. Hereunder I use TV series to get an understanding of the relative importances and durations of progress ranks. The durations are indicative and can be shifted up or down for your game pacing.

Quests/Vows and Explorations

Troublesome : an act
Dangerous : an episode
Formidable : a double episode or a feature film
Extreme : a season (or an arc)
Epic : the whole series (or an handfull of seasons)

Combat

Troublesome : a beat, just getting rid fast of an ennemy or a couple of
Dangerous : a scene
Formidable : a long scene, couple of scenes or sequence. Here the point is to have a shift in the combat, be it a stage or location shift, means, reinforcements, objectives, anything that can redistribute the cards
Extreme : an act
Epic : a whole episode or feature film

In extreme and epic, the way your character experience combat is not continuous as in the other ranks. You play alternatively the combat and inside the breaks and breathing space of the combat. You alternate between combat moves and regular moves to win the battle at the end.

Connections

The rank of a connection shows how frequently they would come back in an arc, a season or the whole series.
A note on villains : you can have epic (or lesser) bonds with recurring villains whose relationship with your character will evolve during play until the end of your character adventuring life. One can think of Q in Star Trek or Murdoc in MacGyver.

Montages

A few moves can be seen as montages :
Battle
Explore a waypoint
Gather information
Set a course
Sojourn (and all the other recover moves)

Momentum

A momentum point can reflect how much the protagonist is ahead of the menace in terms of time (or beats).
1 momentum point can be 1/10th of a second to a second in combat ; or a minute, an hour, a day, a week or a month depending of the rank of the vow.

I think opportunities and perils appearences were a bit lost in translation from Delve to SF and SI exploration moves

Here are a few propositions adding to the moves texts, tell me if if those make sense or not.

Undertake an expedition

Strong hit with a match : you find an opportunity at the waypoint

Strong hit : If there is an opportunity at the waypoint, you missed it.

Weak hit : if chosen, a peril gets in the way of the expedition, en route or at the waypoint. You have to get through it to go further, or find another way. The foe or hazard will not affect you if you do not decide to continue on the same course and go through them. If there is an opportunity at the waypoint, you missed it.

Miss : a peril is coming for you, en route or at the waypoint. You have to deal with it. Dealing with the peril can be a high enough price to pay. If there is an opportunity at the waypoint, you missed it.

Explore a waypoint

Weak hit : you find an opportunity at the waypoint but a peril gets in the way. You have to get through it to get to the opportunity. The foe or hazard will not affect you if you do not decide to go through them and take advantage of the opportunity.

Miss : a peril is coming for you at the waypoint. You have to deal with it. Dealing with the peril can be a high enough price to pay. If there is an opportunity at the waypoint, you missed it.

Thinking about themes : they define the types of perils you will encounter during an expedition.