How much time does it take for a watcher node to sync?
If you don't need the full history, you can easily have it up and running within an hour. In this case you will have details on all accounts and account balances but no details about the whole transaction history prior to the first ledger (block) that was processed by that node.
If you want a
COMPLETE_CATCHUP=true containing the whole history from ledger #1 it will take a couple of days or even weeks (iirc it took me about one or two weeks a year ago). Using a fast storage (SSD over HDD) will significantly speed up the initial process.