Option to randomize delay of delayed page a bit

[xuiqzy]

This is a follow-up suggestion, which likely only makes sense when the countdown timer on the delayed page is not shown anymore (see Idea: Option to hide countdown timer on delayed page).

The suggestion is to have an added delay either by adding/subtracting something from the configured number or specifying the range directly, so that the delay becomes e.g. 50–70 seconds. It should not favor the configured time but just be roughly equally distributed across the possible values / across the range.
The reasoning is that it is then not possible to know exactly how long one has to wait, so one cannot count in one's head to know when the wait is over or think "I'll just have to wait 30 seconds", contributing to more likely wait out the countdown than closing the tab.
If it had to be fixed, for my use case, the added randomness would have to be something like 10 seconds.
Having this as a global option for adding an x second delay to all delayed pages instead of per set would also kind of work in the beginning if per set is difficult to implement.

The idea is also from the Dopanope extension (chrome only).

Thanks for the great extension, it has helped me a lot already! :)