At 5th level, it becomes all-night safety (extended for a 3rd level spell slot and thus 10 hours).
Mind you, depending on the scenario, it'll be reasonably obvious that they're there.
How?
Well, if the group is systemically clearing a dungeon, they probably stop at the last room cleared. A simple Detect Magic and three to eight rounds later, you know where the door is.
The door is invisible, not incorporeal; blindsense or blindsight will notice it.
See Invisibility is a 2nd level spell, and will be available for a level-appropriet challenger wondering why the trail of bodies ended here.
Rope trick isn't usually advantageous in combat. Tiny Hut it Total Concealment for the entire party over a large area, until the opponents close. Great for archers. Secure Shelter provides cover.
If the group is in a forest or other outdoors setting, someone following tracks will have a decent idea of what's up.
Whether their reaction is "lay a trap" of some sort, or remove the trick (dispel magic, antimagic cone, whatever) it's not perfectly safe.
Also, there's a pesky little note in Rope Trick about the hazards of multiple extradimensional spaces.... apply it, then drop a couple of nifties (say, Handy Haversacks; they're cheap enough not to be too unbalancing) into the party. Then have the Wizard roll a spellcraft/knoweledge Arcana check just in time.