Renamed OnSliderAcceptST argument

old: OnSliderAcceptST(float a_value)
new: OnSliderAcceptST(float afSelectedValue)
New naming is more descriptive.
WaitingTimeBetweenInits can be set to 0.0

- Updated OnSliderAcceptST() logic to allow WaitingTimeBetweenInits to
be set to 0.0
- Updated English.txt to reflect this.