Even though BG seemed real time every action was still locked to a 6 second “round” cycle. It was just the turns went so fast it appeared real time. The 2e rules about rounds and turns were respected.
Mmmm... Not quite. In BG, weapons had various hits per second. So, it wasn't really 6 second rounds. Spells also took certain amounts of seconds. Everything had to be adapted for this kind of gameplay.
Now, I will say that I've always kinda wanted to see a variation of turn based where you have 6 second rounds played out in realtime.
So, start of combat. You select spells, attacks, etc. And you pick targets for each character. Initiate combat round. Everyone moves and acts for 6 seconds trying to do what you commanded. It would be kinda like X-wing miniatures. You may not actually attack if your enemy does something you didn't predict.
Example: You tell Gale to cast Scorching Rays on Goblin 1. You tell Lae'zel to attack Goblin 2. You Start Round. Gale begins chanting while Goblin 1 moves. As Goblin 1 moves, he is loading his bow. He gets to a spot just before a tree and fires at Lae'zel. Then he darts behind a tree. Gale finishes his spell but it's too late. It slams into the tree because the goblin made it to cover before he finished the spell. He didn't win initiative, so the goblin was able to finish his move before Gale completed the spell.
Meanwhile, Lae'zel runs forward to attack Goblin 2, but Goblin 2 darts away and loads his bow. He pauses and fires at Lae'zel. Then he runs again. Lae'zel does no attack because the player didn't predict that the goblin would fall back. The player should have used a ranged weapon for her instead.
End of round. Game pauses while you again enter commands and hope you predict your enemies' moves better.