Use a logic_auto with command:
OnMapSpawn > [TF_gamerules entity name] > SetRedRespawnWaveTime ... then the parameter is the value you want. Do the same again, but use Blue instead of Red. This will set the initial respawn times.
When a point is capped, send the command out with the OnCap command, using the same thing OnCap > tf_gamerules (ent name) > Set[TEAM]RespawnWaveTime then the appropriate values you want for times.
I can't give you times, you'll need to figure something out yourself. Look at offical maps for ideas. Just know that if you set the parameter wavetime to something like, 4, that team will respawn between 4 and 8 seconds.