The key with wave starts when not using chip timing (start mat) is that you NEED to know who is starting in each wave.
You assign them a wave group. Very recently in RD, Roger added the feature to assign a gun time to each wave by the press of a button instead of manually collecting their start time and entering it into that wave group. If you have wave groups defined, on the "Set Time" button (use to be the "Gun Time" button), you can now have the wave group picked and when the gun goes off for that wave, it now assigns the time for that wave.
If a person shows up for the wrong wave, you go in and edit their info and put them into the actual wave they started in.