How long after I dipute an item is it taken off my report while going through investigation

It will not be removed until it is determined to be an error.

While they investigate, it will remain on your credit bureau, and it may be flagged as
"disputed by consumer" until they decide the issue.

If it is not true, it will be taken off after they do not get a response from the company claiming the debt. If the company that is claiming the debt replies and tells them yes this is a valid debt it is not taken off.
They don't do a deep investigation, they merely ask the company if the debt is valid

Many people try to dispute all of the listings even valid ones

Agree with Chuck, if the creditor don't respond to the credit reporting agency after 30 days the item is automatically deleted regardless of it's validity.

Carl.-