Hey Hadrian,
This is correct. Risk/complication is reduced the less you lengthen.
Though everyone is different, the average lengthening is 1mm per day. With 5cm, the cumulative lengthening time, hospital, and resting is 3 months and for 8cm, is 4 months.... provided that you are complication free. This is the time frame that you are expected to be able to walk on crutches, hop on the airplane and fly back home. You will need to use crutches for an additional 2 weeks, followed by crane for another 2 weeks, then 2 more weeks before you can fully walk unsupported.
I assume that you are going for tibias. I recommend you go with either LON (offered in China/India and maybe Europe, you need to look this up) or internal precise 2 (if you have money). If you go with precise 2, I believe you can lengthen at home one leg at a time with Dr. M or you can stay near Dr. Paley in the east coast. Paley is the highly recommended route though I wouldn't recommend Dr. M due to his lack of ethics. However, if you go for the cheaper option, the expected time abroad for LON is
4 months LON, for 8cm.
3 months LON, for 5cm
The main problem with LON is knee pain. I personally didn't have it but others have. If you go for full external, the expected time abroad is much longer but you don't have to come back for a 2nd surgical procedure to have the nail removed though I unaware of the length of time that you need to stay abroad. Check Kik's diary. Cheers.