This is a beautiful song I've long admired, yet when the lyrics are studied, it's very difficult to connect their meaning to the title, which is also repeated as the last line of the refrain. I find no apparent tie to the year 1900. So it occurred to me that "1900" could refer to or express military time -- an hour of the day translating to 7 pm. Since couples often dine together in that time frame, it may signify that the hard look at the couple's waning feelings for each other, and the realization that things had gone south beyond repair, may have taken place over a dinner conversation around 7 pm the previous evening. Although the love had faded over time like dissipating smoke from a cigarette, the realization was both sudden and stark -- an epiphany that etched the day and time into the lyricist's mind to the point its significance was immortalized in the song's refrain.