fixed control over duration, lowered min range+doc

[brunotacca]

Addition to #5.
The conditional for duration was pushing it back to 2000ms when below 1000ms.
Users might want more control over the duration (Personal thought, 1000ms was still slow for me).

• Adjusted the conditional statement, fixing the control over the duration.
• Adjusted the lower limit from the duration from 1000ms to 100ms.
• Added more documentation for the parameter duration.

[Bestfastfire]

Thank you for your contribution.