I had a warranty replacement recently, but it wasn't through preferred care so that process may be different! My timeline was
- Saturday morning: Went to an Asurion store, they said I had to go through Google and Google would email me in 1-3 business days.
- Wednesday morning (2 business days later): Email from Google asking for confirmation of the issue, I replied
- Thursday morning: Email from Google to start the replacement process
- Thursday afternoon: Email from Google Store saying replacement shipped with tracking info
- Friday evening: Replacement arrived
So all in all, it took 2 (business) days to first hear from Google, day and a half of processing, day and a half of shipping.