According to Wikipedia:
It entered the American music pop charts in early 1979.
BOS II
This was one of those things that broke late in 78 (I gave it album of the year honors at a dinner at the local pizza parlor) but was initially kind of a cult thing, before it exploded. Just like Chambers Bros is clearly 1967 to me, but 68 in the rest of the country. KSAN played it (SoS) very early.