I have a really long ambient playlist that I like to have in my work space all day... it is generally over 200 tracks long, and over 24 hours of music.
Every couple hours of letting it do it's thing, it will stop... generally around 2 hours or so into the mix. If I start the mix back up where it left off... same thing, 2 hours or so later it stops.
I am using the desktop application of Spotify, Free Plan, in the United States.
I am running on a MacBook 7,1. 2.4GHz Intel Core 2 Duo running Snow Leopard.
For the need to run legacy software, it is not an option to upgrade the OS or anything like that.