It’s often useful to postpone pv‘s calculations until there’s data flow for real. As man page says:
-W Wait until the first byte has been transferred before showing any progress information or calculating any ETAs. Useful if the program you are piping to or from requires extra information before it starts, eg piping data into gpg(1) or mcrypt(1) which require a passphrase before data can be processed.
I have had difficulties with remembering that option until I’ve gotten it as “White rabbit”. Now it’s an ease.