=if(B1=0,"","Classroom date: "&text(B1,"mm/dd/yy")& " Held at: "&B2&" "&B3&", "&B4&" From: "&B5& " to: "&B6)
If B5 & B6 are times
=IF(B1=0,"","Classroom date: "&TEXT(B1,"mm/dd/yy")& " Held at: "&B2&" "&B3&", "&B4&" From: "&TEXT(B5,"hh:mm")& " to: "&TEXT(B6,"hh:mm"))