Question about flower?

Hi my plants 75 days old from seed, at day 80 I'm going to put it I to flower. It's in a 5 gallon bucket right now and I'm just wondering if this is going to be big enough that the plant isn't going to get root bound during flower. Its also about 8"at the tallest point

You should be fine. 5 gallon is commonly used.

no worries, all of our indoor plants have boundaries aye?
none are grown with an infinite space for roots to travel. We all see big root plugs in any size container when we're done, smashed right up against the sides of any size container, if you're doing it right so shall you!
poke a hole or 2 in the bottom for drainage.

You train that plant ? If so I like, I prefer small bushy plants.