Everything in Kingdoms of Camelot takes real time.
Time is the biggest limiting factor in the game.
Eventually, things will take many hours (or even several days) to complete.

You can shave off up to 10 minutes if you are willing to pester your friends (select “Upgrade With Help” when building).
Knights are a BIG help when assigned to appropriate roles (see “How do I use Knights?”).

Also, you can research Giant’s Strength to speed up construction of buildings in the city and fields