Harmony: Seasons of Love, Rent

Seasons of Love, a song from the Broadway musical Rent, has probably the most well-known line from the production: "525,600 minutes, 525,000 moments so dear, 525,600 minutes, how do you measure, measure a year?"

One interesting thing about Seasons of Love in terms of harmony and melody is that for almost the entire first half of the song, it is sung in unison, the only harmony coming from the piano accompaniment. Then, once it first makes the switch into vocal harmony, there is very little, if any, unison singing.

The vocal harmonies start at 1:05 and continue almost uninterrupted until 2:58, going into unison or a single singer from 1:24 - 1:26 and again from 2:08 - 2:21.

The harmonic rhythm goes very slowly through the chorus (first heard at 1:09 in this video), quickly through the second male/female split (first heard at 1:31), especially in the male part, and moderately fast through the verses, where there is one prominent soloist and the other singers make vocalizations under them.
During these verses (from 1:37-2:10), the harmonic voices imitate instruments very softly, giving focus to the melodic line.