Monster Legends features a variety of buildings and structures to choose from. Each structure requires a gold or food cost to build, and a worker or friends to open it.
Some buildings can take days to complete, but generally this only occurs later in gameplay. A few buildings instead require a certain amount of friends to be hired to activate the building.
In most cases if you need friends to help open the building there is no wait time for construction. As soon as you purchase it the structure is completed immediately, and can be opened as soon as the required friends assist you or you buy out the slots with gems.