Trying to control bed temperature at end of gcode

[4truemodels]

Hello!

We've noticed for long that every glass bed we use to print with 90ºC and above has a really high chance of breaking whenever it finish printing and cools. That issue is not a serious one in Summer or with a temperature above 25ºC, but now the cold is coming to us we pretend to try some changes to minimize the damages.

We thought it would be a good idea to control the way and speed the heated bed cool down after finishing a print job. In order to do so we planned to insert some orders at the end of the gcode (very easy to do within Cura), like this ones:
M190 S90;
G4 S60;
M190 S80;
G4 S60;
M190 S70;
G4 S60;
...and so on until reaching a bed temperature of 40ºC to finally set the heated bed off.

We tried to do that with no success wherever we put that orders at the end of the gcode. However, every test we did at the start of the gcode, before M82 command, worked perfectly and controlled the temperature as we want including some pauses betweeen with the G4 command.

Please tell us how can we set those orders at the end of the gcode to make them work. We really think controlling the speed in which the glass cools down will make a difference in the amount of breakings per week.
Last year we had to discard printing with temperatures above 60ºC through last weeks of Fall, and all Winter, because we got even 3 glasses broken per week when printing above 80ºC.

Thank you!