>Well, to me the re-factored command is much easier to understand and debug. But it's up to you to take the suggestion and try it or not.

This would be better:

...
     WHERE BusinessTime.NoProvince=
      (SELECT COALESCE((SELECT Company.NoProvince FROM Company WHERE Company.NoCountry=1 AND Company.Numero=Client.NoCompany),84)) AND
      BusinessTime.NoHoliday=0 AND
      BusinessTime.Start<Client.FirstDate AND
      BusinessTime.[End]>=Client.SecondDate) Temp)
...