Re: RC Oscillator
It depends on the RC oscillator and the components used to build it.
Yes, temperature variations cause the frequency to change, but that is because some parameters of the components change: values of resistors and capacitors, leakage currents of capacitors and transitors and so on. Supply voltage and humidity are factors, too.
But the actual changes can be smaller than the phrase "5% to 50%" suggests. Because everything has to be characterized over a certain range of operating conditions. If the oscillator has to function only from 0°C to +40°C, the change in frequency will be smaller than if the range is -40°C to +125°C.
I do not know what the interruption in program does, so I cannot tell if you can use the RC oscillator or not. If you are referring to the internal RC oscillator of a microcontroller, then you can do anything you want. The frequency of the oscillator will not affect the functionality of the program, only the execution time and the timing of the pulses it generates, if any. So, if you use the program to generate any sort of timing, you need to take into account the accuracy of the oscillator and decide if it's satisfactory for the puspose.