Hi, the reason behind this is that opacity, believe it or not, does not go straight in 1, 2, 3, 4 numbers but for example from 1.1231 to 2.3424 then 3.4145 and so on with totally random values after a dot.
You can work this out with System->Is between values.
This would be something like:
timeTravelable.opacity
69
71
Try this and manipulate values to see if it works : )