How long after transplanting would it be safe to t...

It really all depends on how the plants react to the transplant. What I find really helps my plants recover from a transplant is using some real growers recharge to give the roots a boost to start growing into the new media. Ive had plants not even slow down their growth from a transplant and was able to top them 2 days after transplanting without any issues. If the plants seem to be slow growing after the transplant give them like 4-5 days to recover and start growing quickly again before topping. That will alow the plant to have low stress levels and have a bigger more established root system which will help it recover from the topping better.