I imagine it depends on how many clients you have and how large their data files are.

Anywhere from 5 minutes to 5 days --------------------------- that should pretty much cover the unknown part of that question 😀

Sorry, we already have a Lisa here.  She's probably commented on many of the threads that explain why it's a big mistake to roll over all the clients this early in tax season.  

Set your timer. Transfer one client. Check timer. Multiply that time by the number of returns you are transferring.

ProConnect is designed to be able to proforma clients to the 2025 quickly.  Depending on the size of the returns, some can take longer but should not generally be longer than a few hours.  If you have triggered the process, and it has been more than 24 hours without all files completed contact our support line so that we can assist you with completing the process.