Null disable at specific time?

Oops, looks like I wrote a response yesterday, then never posted it. Mylenium said the majority of it, but if you are looking to animate parenting, then there's a script called Good Parents that does exactly this, but it does cost $30: https://aescripts.com/good-parents/

Unless the "parenting" is completely faked with expressions to begin with, then no, there is no way to control this. Not a problem, though. Nothing stops you from pre-composing the whoel shebang and splitting layers to unparent them or any number of these methods in any combination. Similarly, more complex hierarchies with multiple intermedate levels of parenting can easily work around this issue by creating virtual transform groups in a sensible fashion and then only moving those subsets of layers or applying compensatory motion even if they are parented further more upstream in the hierarchy. Realyl a lot of ways to do it before even resorting to expressions, which would require much more specific explanations of what you are trying to achieve, anyway. So start by structuring your project accordingly and try the things I mentioned. For anything more, proper details and screenshots will be required.

Mylenium