Not everything at the table is a scene. Some of what happens between the interesting parts is worth playing out in real time, and most of it is not — the skill is telling the difference quickly, without stopping to think about it. Travel, light, hazards and rests do not have their own rules on this page; the player chapter already covers what each of them does. What follows is what they do to your pacing, which is the DM's problem alone.
Ask one question before you narrate a stretch of travel: can anything go wrong on it, and is anyone deciding anything. If the answer is no to both, say so in a sentence and move on — a week on the road that passes without incident does not need a week of table time. The moment either answer flips to yes, it stops being travel and becomes a scene, and you run it like any other: describe the situation, let the players decide what they do about it, and see what happens. The rules that govern movement, light and hazards along the way are on Exploration; this page is only about deciding when they are worth reaching for.
Light is not a fact about a room that you look up once and forget — it is something you place, the same way you place a monster or a locked door. Bright Light, Dim Light and Darkness are the three settings you are choosing between whenever you decide what a torch, a window or a shut door leaves behind. What each one causes is the part worth planning for: dim light leaves a space Lightly Obscured, and darkness leaves it Heavily Obscured — the second is a far bigger deal than the first, and it is worth knowing which one you are setting up before you commit to it.
Check darkvision before you set the scene, not after. A dark room is atmosphere to a party that can see through it and an obstacle to one that cannot, and those are two different scenes to run — know which one you are building before someone opens the door.
A hazard is damage with no creature behind it, and the two that come up most often are falling and suffocation. Both are entirely avoidable and both are entirely unforgiving once they are not, which is what makes how you present one matter more than which one it is.
A hazard the party can see coming is a decision: cross the crumbling bridge or find another way round, take a breath before the door seals or do not go through it yet. A hazard they cannot see coming is just a tax on whoever fails the roll. Prefer the first kind wherever you can — telegraph the cracking ice, the sinking floor, the door grinding shut, before it happens. The danger loses nothing by being visible, and seeing it coming is what turns it into a choice instead of a trap you sprang.
The player chapter tells you what a rest gives back; here is what it does to you. A Short Rest is the lever that turns one dangerous fight into several in the same day — spend an hour and the party is most of the way back to full, ready for whatever comes next. A Long Rest clears the board entirely and starts the day over.
Which makes how often the party gets to rest a bigger difficulty knob than any monster you choose. The budget on Building an Encounter assumes a party that walks in with its resources intact — the same fight against a party that already burned two Short Rests' worth of spells and hit points, and one that spent none, are not the same fight, even though not a single monster changed.
Deny the rest for long enough and you get Exhaustion, which is what accumulates when the party pushes on past the point where they should have stopped. It is the cost of that choice, not a separate danger you added on top of it. The loop all of this sits inside — description, decision, result — is on Rhythm of Play.