Hutkikz:
When using subtraction on unsigned integers. the subtraction will automatically handle it.millis() - startTime >= interval Lets try it using byte to make the math easier
10 - 245 >= 20 Millis() has just rolled over startTime was before rollover
if you start at 10 count back to 0 then 255 on down you will see that the answer is exactly 20.
subtraction will always give the right answer when using unsigned integers hence no problems with rollover.
GREAT!! Thank you all of you!!