I have tried different values for this with no success.
First the M0 command were not working.
Then I decide to substitute de M0 command by a G4 P6000 to, at least, have some time.
This week the UM3 has received a new firmware and then the M0 command has started to work but... now the problem is that the tempertature decreases while M0 command is alive awaiting. Even if I put the two temperatures in the script dialog equal to the working temperature the fact is that goes down during the pause.
Yes, of course, prior to restart the printing temperature reaches the working temp, but the next layer does not bond well with the previous one, so after some layers that pause layer breaks.
Anyway, many thanks for your help