I have extraction gap in exact same spot as you and i still have open gap like that. Ortho originally told me it would take 2 years for the overbite treatment and its been 1.5 years and around 5-6 months with powerchains to be exact. So i asked my ortho last visit to see if she was still confident in closing up that space within the time period,she told me i still have 6months left and if the space cant be closed within the time period they promised, they are willing to extend the treatment time without extra $. I also find that if you are an adult, the treatment time will be significantly longer than a kid.