Following the recommendation in the item's description, make a backup of your database
1/ Run the transitioning tool. This will close your forum for you while the tool is running. When it is done, it will re-open your forum. 2/ Upon completion, follow the page link at the bottom of the page which tells you to now enable the "MySQL Full Unicode Support" setting.
The time that the transitioning tool takes for processing is based on many factors that i would have zero way of being able to answer for you. Once it is started, it will display items as it progresses through them. The item which will take the longest is the posts table. you'll know when you get to it because the page will continue working - the display will look paused, but its still working. When done, it will tell you its done. I've run the tool on a 2.5gb DB in under 5 minutes, and then rerun it on a restored backup for a completion time of under 10 minutes. But that was a shared WINNT machine with MariaDB 10.4. The tool changes your table's collation. It does not change your data. But a backup is always advisable when you work on your entire database.