I was told this should take “enough time to drink two beers.” I can’t imagine the wuss who came up with this. I usually put down at least three and often four doing the roux. It’s about half an hour, if it takes more (up to 45 minutes), don’t worry.You really need to error on the side of caution here because if black burned flecks appear in the roux, you’ve fucked up and burnt it. You have to start over. Seriously. It’s ruined. So stir constantly and be patient.