Yes, it would be good to know how long we have to prepare.

 Tarja stays away from the mechanical trap preparation, and instead looks for narrow areas where the intruders could be ambushed or cornered.

Can't say I like these goblins much, but I don't like those hobgoblins either, might as well deal with those guys when they get here...

Arvel points at Ethan.

"Yes! I love where your head is at!"

Zeke spins out his blade to it's full length and begins pacing the edges of the room - clearly itching to hit something more his size after the encounter with the Dragon.

'Traps are fine, but whatever we do we need to do it quickly, I fear they may return any moment.'

Yeemik shrugs "could be any minute, could be another hour."  (I'll do a roll for it and will let you know if it's officially an hour with regard to a Short Rest for Tarja, etc.)

The goblins show Ethan and the others that they've piled a good deal of stone atop on of the walls and it could easily come tumbling down if triggered properly.  It could certainly hurt a good deal of foes if they were tightly clustered, but would be hard to aim at more than a 10ft square.  The goblins have it reinforced with a few extra boards running to the floor at the moment.

"I'll take Gundren and the shield back to the throne room," Elra says, "unless you want to stow the shield away Ethan?"

Fae would have taken her time to get back to the castle, she was in no hurry to return to their smell. She'd stand outside the doorway to call Edgar back from his scout. Once returned safely inside the walls of the castle, the wizard would offer Arvel and Ethan her Mage Hand if it could be of any assistance at this point. By actively interacting with her teammates, it'll keep her mind grounded in the present so she will be prepared should the hobbs come.

Ethan looks over at Elra, from his examination of the trap.

"Oh I can stow the shield, if you are done with, uh, him?"

As Fae returns and offers her help with her mage hand spell, Ethan remarks,

"Oh that could work! We could rig the trap so Fae and activate it with here mage hand spell."

"Then no one needs to be up on the decidedly dangerous looking wall to trigger it."

"Hmm, we could even run the trip line along the top of the wall so it can be pulled remotely, but further along from the trap, so you're not underneath it yourself."

"I'm not done talking," Elra says, "I just didn't know if you wanted to put him away." She gently picks up the shield and helps Gundren up, taking him back to the throne room.

Yeemik comments "they aren't going to go there."  "Everyone knows not to walk there.  They'll lock their wargs up outside and go through the dining hall."

(Sure, Tinker's Tools works if you feel that is the best option.  DC10 is fine if we're just re-running the trip wire, maybe extending it, etc.)

"Oh...hmmm...well maybe we should have a look at the dining hall instead?"

Ethan looks to Arvel and Zeke, then to the others, hopping for ideas or recommendations.

"If you can get them to let there guard down in the dining hall," Elra says, "we might be able to deal with them easier."

Fae would smile, glad she could offer some help to Ethan and Arvel's quest to set up a trap. In response to Ethan's question, she would nod, agreeing with him and Elra's suggestions. "If it's possible, let's do it quickly." She'd glance over, checking on Zeke and his pacing.

Ethan nods and turns to Yeemik,

"Could I get help from you and your friends?"

"If we all work together we can try and relocate the trap to the dining hall."

"That way we can catch them unaware and unprepared for a fight."

Zeke stands behind Ethan as he speaks to the goblins - his size adding weight to the artificers' request.

'That might have sounded a lot like a question. but I wouldn't let myself get confused'

Arvel begins summoning the illusion of Grol, pacing back and forth muttering to himself as he gets into character.

Ethan give me whatever you feel is your most appropriate skill check, with Advantage since you have help.  Sliding scale here with regard to DC... an extremely poor roll might result in a goblin getting killed in a collapse of rubble, while a great roll will not only mean success but also completing the work rapidly.

After that we'll make a roll or two to see when the hobgoblins arrive vs. the engineering work and the chance at a short rest, and go from there.

If Ethan is successful and Arvel is Grol, what will everyone else be doing in preparation or when more foes arrive?

Hope everyone is doing well in real life!

Fae would shadow Ethan, providing assistance as necessary. She'd use her Mage Hand as required, following the artificer's direction. Should her magic hand be required to set off the trap, she'd go over the plan at least twice to ensure she would be ready for when the foes arrive.

Ethan gets to work assessing the trap and then the dining hall and directs the goblins and any of his friends who are helping, in the deconstruction and reconstruction of the trap into the dining hall.

Tarja would look for a good place to engage the Hobgoblins - a place where she and Zeke would be able to stay between the Hobgoblins and the rest of the party. Maybe a narrow corridor, or a place for an ambush, or something like that.

Elra will take Gundren and the shield back to the throne room, and set Gundren up with her bedroll and blanket before looking for a place to wait in case the party need her help.