This is the baseline. If you've got a song and a beat and you want to put it out properly, this covers everything between those two points.
Two hours is enough for one song if you come in prepared — beat sent ahead, lyrics finished, you know how you want to sing it. If you're still writing in the booth, look at Release Ready instead, which gives you four hours.
Light mastering is included rather than full mastering, and that's not a downgrade — because we mixed the song, we already know what it needs. Full mastering exists for mixes that didn't come from us.