UBB.threads PHP Forum Software Community Forums UBB.threads 6 Version 6 Support Time of Upgrade from 6.3.1 to 6.4.2

I'm wondering how much time I need to allow to do the upgrade between 6.3.1 and 6.4.2. I have a very active forum and there are around 700,000 posts and what I am really asking is how long I should expect the altertables to take?

Thanks,

Chuck Weinstock