Objections to Guardian Ad Litem Report

I was doing some reading on guardian ad litems a few days ago and started doing some thinking.  When is the time to objection to a guardian ad litem report?  After doing some thinking, I think formal objections need to be made in written form prior to trial and then those objections need to be renewed at trial.  By making the objections early, any deficiencies may be remedied which could change the opinion on the case. This is similar to me in making a Daubert challenge.  I am aware of at least one appeals case pending concerning when these should be made and whether waiting until post trial to make the objections is sufficient or counts as a waiver.