Potter expansion will start before Shrek replacement, as it has the most work to be done, yes. But it's not like they have to drain and tear down JAWS. It's just an open air theater to demolish at least.
How long did it take to build Transformers again?
Okay, fine, that was a clone...
How long did it take to build Volcano Bay then?
It can be shocking how fast they get these things done.
Add in that it's also kind of being built during a void:
EU hasn't really started pace yet as it's still in pre construction mode.
SeaWorld and Busch aren't building anything.
Guardians appears to be almost finished.
Tron only has 2 workers on it.
If you're wanting to build a ride quickly, now is the time to do it.
Even more on top is that if the crowd levels are low and not really expecting to pick up until next year, with Shrek in the middle of the park, it's the perfect time.