Hey Hamilton. How long it takes depends on a few things, mainly method and distraction rate.
Distraction rate varies person to person, and also differs depending on tibia or femur; tibia generally going a bit slower at 0.75 mm per day vs 1 mm on femur. If you're doing 5 cm tibias and 7 cm femurs, it'll take 66 and 70 days per segment respectively.
Your second surgery will commence after consolidation and restoring your gait (manner in which you walk). Externals-only means it'll take another 60 days until consolidation, and you'll be wearing those frames the entire duration. LON and LATN patients will have their frames removed after distraction, and consolidation should take roughly 1/3 of distraction phase. So if you lengthened for 70 days that's ~23 days of consolidation, add a month for weight bearing and restoring gait, and you're back to do your second set of segments.
Assuming that you're doing LON and everything goes smoothly and you keep up with your physiotherapy, it's roughly 8-9 months. You'll regain muscle strength and range of motion in 1-3 months. Return to sports in 4-6 months after the last surgery.