Hello A.,
See the history and similar request or wanted feature here:
Awaiting her implementation... If that can help,Regards,Th.
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You can now use:
printscale weekly with calendar date
With that:
@startuml printscale weekly with calendar date Project starts the 6th of July 2020 [Task1] on {Alice} lasts 2 weeks [Task2] on {Bob:50%} lasts 2 weeks then [Task3] on {Alice:25%} lasts 3 days @enduml
See: