I would top around 4th/5th node if the plant is otherwise healthy and thriving, if it seems weak or has any issues it's better to wait for it to become stronger so it will recover better, but I wouldn't wait past 7th node for it. If you veg for 60 days, you can also top/fim more than once, given your plant recovers well after the first time. Make sure to also give enough nutes (nitrogen) to support lateral growth, she might get a little hungrier after the topping. I hope this was helpful :)