So, one bit at a time:
[sblock=RE: Alrough]For this scenario, the party closing the rift would probably be the focus of the "adventure." To save the city, they assault the daelkyr clustered around the rift and pull it shut. The four-person party above might have to find the item that can seal the rift (exploration/interaction), and then fight off the daelkyr between them and the rift (combat) until they reach the goal, seal the rift, and get to take an uninterrupted rest. If the party rests before then, the daelkyr replenish, or the artifact goes missing, or they move the rift (or open a second one!).
You could also break it into smaller bits, if you wanted a longer event in the campaign. You could have them secure a part of the city, to defeat enough daelkyr and build enough fortifications and save enough townsfolk that they can mount a counterattack -- or at least get a night's sleep. If they sleep before they've secured the zone, they get attacked, or the daelkyr replenish.
For this one, you can do it a few ways, too. The first one that jumps to my mind is to say that the adventure ends when they reach a point at which they can rest easily for the night (like a fortified town), and then put the encounters in between them and their destination (6 bandits, 4 starving wolves, and a vicious thunderstorm!).
If the party tries to retire early, the adventure recharges by more wild creatures or dangerous highwayfolk finding the adventurers, either while they sleep, or during the next day.
You could extend the journey out for longer by putting multiple "adventures" in between the party and their destination. If rests are on the days/weeks timescale, you even can end up with something very much paced like LotR, with long periods of wilderness travel punctuated by occasional civilization where the party can recover for the next leg of their journey.
It's not meta-game -- a DM in designing an adventure probably should have goals for the party already (or the party should have given the DM goals, like "We want to go to the Free City of Greyhawk,"). All this is doing is saying that there's going to be a set of challenges (encounters) between you and your goal.
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*whew*
Time for a drink.