Set the finish around your return arrangements
Before starting the visit, note the return transport you intend to use and your airline's required times for the airport steps relevant to your booking. Include any extra stops for your bags and the journey to the terminal for your flight in that plan.
Set your own time to finish shopping from those arrangements, and decide which shops can be dropped. When that time comes, leave the remaining purchases for another visit.
For any meal or shopping you leave until the airport, use the directory for your flight’s terminal and the area you can reach before or after security. Kansai Airport’s dining directory separates those locations. Check the relevant facility’s hours for your date, then fit that stop into the return plan you already have.