Adjust block time (adjust slider)

[Jeroen-Schreel]

Is your feature request related to a problem? Please describe.
The slider to adjust length of blocking time always annoys me.

Describe the solution you'd like
It would be a lot easier to have an input box to block, e.g., 3h, rather than using a slider which is less exact. Maybe both options (slider and input box) could be made available?
Also, sometimes I just want sites to be blocked until a certain time, I think it wold be very useful to be able to put in a deadline, e.g., block until 5pm.
Both options could be implemented with 2 small input boxes, where input in 1 box disables the other box and/or slider.