Allow wait time personalization

[bNobo]

Is your feature request related to a problem? Please describe.
There are situations where user could need a personalized wait time. For e.g. when he hears there will be a meeting in 30 minutes or when he needs to reboot its computer while there are only few minutes left, see #9. In these situations, there is no suitable choice because the selection is limited to 45, 60, 90 and 120 minutes.

Describe the solution you'd like
There should be a slider on the "adjust wait time" window in order to allow the user to select a personalized duration instead of a predefined value.

Describe alternatives you've considered

1. put the slider on the popup menu instead of "adjust wait time" window but I don't know if it is technically feasible and it seems to me that it is not the most user-friendly solution.
2. change computer time to mislead the countdown :/