Does it then take a while before it starts to drop, waiting for the gas to be consumed down to the level the needle is?

Don't know on yours, but I've bought a Gen II sending unit for something like $60 maybe, and a Gen I 4-cyl for like $35.

Big Truck: 00, 3.5, Endeavor, 5-Spd drive line in hand!
Little Truck: 87, 2.6T I/C, MT, LSDs, Tonneau Top
Her Truck: 03, 3.8, 20th Anniv, 65k
Daughter's: 06 Eclipse, Keeping it Mitsu!
FSMs: MitsubishiLinks.com