Please refer below snapshot, where 'Set up SSO' objective start date has been changed to 15th JAN 2019, but start date of underlying task did not changed. (e.g. Send customer SAML Metadat)
I have tried this in different org and it looks product bug.
Most of the clients using Success Plan complaining on same thing, as it is not feasible to change start date of each and every task.
Best answer by aditya_marlaView original