A page waits 80 ms for session, then serial independent calls of 220 and 350 ms, then renders for 70 ms. Estimate the benefit of parallel calls and state when it is invalid.

Original arithmetic derived from the supplied independent-call timing assumptions: serial total is 720 ms. Parallel estimate is 80+350+70=500 ms, saving 220 ms. The change is invalid if one call needs the other's result or if parallel demand violates capacity or authorization sequencing.