Well every yeast strain is a bit different but normally the range is fairly forgiving. Speaking from homebrew side; killing yeast from cold is almost impossible.
Homebrew side; they make electric thermostat controlled blankets to control temperatures; if you are going repeat this a couple times might be worth investment. In beer world; changing the yeast reproduction rates and brew temp can have significant effect on flavour; not sure this applies to sourdough starters at all.
above 108F - yeast start to die
140F - all yeast dies
below 32F - yeast can die
40F-65F - most yeast strands will be sleeping / dormant
78F - usually optimized production
Now I see optimized production of CO2 change from 10-15 degrees depending yeast strain; some being as high as 100; others being low as 70; but gives a good idea.