Well Im no legal expert but perhaps the reason Caseys defense wants complete results of the 1st autopsy is so they can know what they might need to defend. Remember the onus of proof is on the prosecution to prove their case beyond a reasonable doubt. The defense may have done little or no testing prior to access of the 1st autopsy results - perhaps they want all the results so they can conduct testing to disprove the 1st results.
If for example the 1st autopsy results revealed trace elements of some type of drug or sleeping aid (pure speculation), then that might form the basis of whatever theory the prosecution presents regarding how Caylee died. Forsenic examinations are very complex and based on science - statistical probability and analytic opinions - rarely is there 100% proof of anything. So the defense might try negating whatever was found with an alternate innocent explanation, or try to have the entire 1st autopsy results thrown out as inadmissible evidence based on some procedural irregularity. So it would seem to me they would want the remains so they could conduct further testing, if they so chose. This is simply my opinion.
But therefore I think the defense should be given as much time as needed - if that amount of time is unreasonable ie months, it would be the court who would intervene. The defense teams release - its all procedural legal process. If Caseys defense is not allowed adequate time then the 1st autopsy evidence will be tossed out the window....and potentially along with it the entire case as well. The Anthony family has no choice but to wait.