Should piston be at top dead center when timing marks mesh on a single cil 18.5 intek briggs and stratton engine

Hi,
That is not stated anywhere I know of in the repair manual. Take into account that the manual does state that the piston should have dropped down 1/4" past TDC on the compression stroke to properly adjust both valves. This is to assure that the ACR (automatic compression release - for slow speed cranking) is out of play. I wouldthink that it would be about there as that would also assur that the valve springs do not interfere with the installation.
Peace,
Clarke