How much does it typically take a studio to do a 4K restoration?

Your question really has nothing to do with formats, and last I checked, they shoot content in studios, but they don't restore them there. Aside from that, you're asking in very general terms, and the only answer is "it depends."

How do you define "restoration"? If you're talking about repairing damage, then the amount of damage and how much money you have to spend are major deciders. You could hire a team of artists to recreate each damaged frame, doing background work in each and every frame, and it could take a lifetime and a king's ransom. At the other extreme you could run the DI through whatever scratch & lint software is handy and churn it out on your home computer for next to nothing. Needless to say, the distance between X and Y is immense.

All other things being equal, 216,000 frames is more than 144,000 frames. When the film was shot is immaterial unless you're talking about some specific age-related defect. If you are, then it really helps to know what defect(s) there are. Without that knowledge it's so hypothetical that it's hard to take seriously.

I believe Lawrence of Arabia took a year-and-a-half. It's a long film, shot in large-format Super Panavision 70, and needed a lot of cleanup work, most notably the middle act, where the negative literally got melted by the blazing desert sun.