when is a doctrine of laches used…and how does it work

It an equitable doctrine that can be used as an affirmative defense to a claim, it is used when the defendant can allege that the moving party or plaintiff unduly delayed in filing his or her claim and the defendant is prejudiced by that delay.

1.what is a plantiffs defense to latches? 2. If I am filing issues within the statutes of limitations of the contract can laches be used as a defense effectively?

I cannot predict the outcome on any one case, but your rebuttal to any defense of laches would be that your delay was not unreasonable given the circumstances, and that it did not prejudice the defendant.