Mathematical operations on the type Period?

Hi,

We would like to apply an automatic "efficiency" coef to developper estimations.
In our dev team we are used to estimate tickets in hours, and then apply a efficiency coef to this estimation (ex : 70% efficiency will give a final estimation of 7 hours for an initial estimation of 5 hours)

I managed to do this before with "int" fields (with workflow editor), but with the new Period type I cant find how to perform mathematical operations. Is it possible ?

Regards,

Mael