Originally posted by NiceGuy:

1 and 2 start wolfs only spawn at night. They will despawn at dawn/day but only if you leave theire render distance. This ALSO is for tamed night spawns! Only breed children from 1 and 2 start wolfs do NOT despawn at day.

Not true. They fixed this ages ago.
Our 2-star did not despawn at all, neither when leaving the site (was withing workbench-radius, though), nor after we tamed it and walked it home during the day. It got trapped at night, tamed both during the day and night, and we probably still have it, although we lost track after 3-4 children.