New Duration type

Setting up a task assignment for multiple roles with a 10 Planned hours ammount and a custom proportion eg.:

10% for Account Manager (1 hour)

20% for Copywriter (2 hours)

50% for Multimedia Designer

30% for Social Media specialist

...and I modify the Planned hours let's say to 20, the assignment could follow proportionally: 2 hours for Account Manager, 4 for Copywriter...,

If 25, it should be 2,5 for Account, 5 for Copy etc.

Currently I could not find such a way.