how long should it take to transfer this material from a PC to my Mac?

Depends how much data you have.

Here are some other ways to move the data as Migration Assistant occasionally has an oops.

Windows Data Migration

Windows File Migration

ned burns wrote:

How long should a data migration from a PC to my Mac take?

Depends how much data you have.

And how you transfer it, if you chose wireless (for the convenience) you have chosen the slowest possible method, hours will pass.