The 'later' and 'soon' options in the building construction menu is miss-leading.
Reasons why you can't build in 'later' include 'you are only allowed 1 of these buildings' which should really mean 'never'
'Soon' should mean 'when you have built up enough resources.
Perhaps remove the 'later' option if we can't give it a sensible list of buildings?
As a developing empire, I never found the 'later' option helpful. So, I'd cull it.
I like 'soon' the way you have suggested it.