It depends on a few things....here's how it works. You have to have a "material change in circumstances" i.e. a reason that the court should change it's order. It has to be something that if the court knew then what it knows now, the order would have been different. Depending on the nature of what you are trying to show as a "material change in circumstances" is what depends on your time period of documentation.

For example, you are looking for a decrease in child support, you need proof that your income has changed, it was not voluntary and it will last for six months or more. So, if you have a business for example, and it has been slowing down, you may need documentation of more than six months to show that it has had a gradual decline and is likely to continue.

A situation where you want to show that the mother is in contempt and refuses to follow the court order to the detriminent of the child's health or well being, could take years of documentation.

An immediate safety risk or concern, you need only have current documentation that it's a risk.

There is no specific timeline, it's mostly (and don't take offense to this) common sense. Think about what you are keeping documentation of....if you were a judge, what kind of pattern would you expect evidence of before making a ruling. Some timeframes are shorter than others depending on the needs of the parties and the best interests of the child.

It's hard to answer these questions because the reality the answers are often too vague. What I will tell you for sure is this....if your documentation preceeds the last time you had an evidentiary hearing on a child support/custody issue, it's really no good because you should have brought it up at that hearing. So if there has been a modification in the last three years which is after some of your documentation, throw that documentation in the trash because more often than not the judge isn't going to look at it. It's almost like, speak now or forever hold your peace.