[marcoszorrilla]

He estado desarrollando la excelente idea de Román y he llegado hasta sumar horas y minutos, lo he dejado ahí, porque me parece que el código deviene demasiado farragoso.

select
  extension,
  sum((
	 cast(substring(cast(tiempo as char(8)) from 1 for 2) as Integer)*3600 +
	 cast(substring(cast(tiempo as char(8)) from 4 for 2) as Integer)*60 +
	 cast(substring(cast(tiempo as char(8)) from 7 for 2) as Integer) 
  ) /3600) as ttHoras,

  
	  sum((
	 cast(substring(cast(tiempo as char(8)) from 1 for 2) as Integer)*3600 +
	 cast(substring(cast(tiempo as char(8)) from 4 for 2) as Integer)*60 +
	 cast(substring(cast(tiempo as char(8)) from 7 for 2) as Integer) 
  ) /60)   -

	 sum(((
	 cast(substring(cast(tiempo as char(8)) from 1 for 2) as Integer)*3600 +
	 cast(substring(cast(tiempo as char(8)) from 4 for 2) as Integer)*60 +
	 cast(substring(cast(tiempo as char(8)) from 7 for 2) as Integer) 
  ) /3600) * 60)  as ttMinutos

from 	"d:\pruebas\ruben.db"
group by
extension

Dada la casi nula posibilidad de sumar tiempos con Pardox, yo crearía una rutina, para hacer las sumas mediante un bucle, la acumulación dependiendo de los casos, pudiera ser en un StringGrid, o en una tabla creada al efecto.

Un Saludo.