This property of the Project object tells you when the project was last built.
tLastBuild = prjProject.BuildDateTimeBuildDateTime gives you a programmatic way to find out when a project was last built. It shows you the same information that's in the Project Info dialog for "Last Built:". The value returned is a datetime. If the project has never been built, you get the empty datetime ({ / / : : }).
IF TTOD(Application.ActiveProject.BuildDateTime) < DATE()
WAIT WINDOW "Haven't built this project today" NOWAIT
ENDIF