[RFE] Allow specifying override duration with `fbrnch build -o`

[gotmax23]

I think the title is self explanatory, but let me know if you need any other details. Thanks!

[juhp]

Okay that seems quite reasonable.

Though would it be better to lengthen the default used duration?

[juhp]

I have implemented this locally - I will commit it soon: so it should be in the next release.

[gotmax23]

Thanks!